Ultraviolet laser apparatus and exposure apparatus using same

ABSTRACT

An ultraviolet laser apparatus has a laser generating single-wavelength light between infrared and visible, a fiber optical amplifier for amplifying the laser light, and a converting portion converting the amplified laser light into single-wavelength ultraviolet light, using a non-linear optical crystal. An exposure apparatus transfers a pattern image of a mask onto a substrate and has light source including a laser apparatus for emitting laser light having a single wavelength, a first fiber optical amplifier for amplifying the laser light, a light dividing device for dividing or branching the amplified laser light into plural lights, and second fiber optical amplifiers for amplifying the plural divided or branched lights, respectively; and a transmission optical system for transmitting the laser light emitted from the light source to the exposure apparatus.

This application is a continuation of PCT/JP98/05367, filed Nov. 30,1998.

BACKGROUND THE INVENTION

1. Field of the Invention

The present invention relates to a laser apparatus, and moreparticularly it relates to an ultraviolet laser apparatus for generatingultraviolet light capable of suppressing generation of speckle with lowcoherence, such as an exposure light source used in a photo-lithographyprocess for manufacturing micro devices such as semi-conductor elements,liquid crystal display elements, CCD and thin film magnetic heads, aswell as relates to an exposure apparatus using such an ultraviolet laserapparatus.

2. Description of the Related Art

As information technology equipment has progressed, regarding integratedcircuits, improvement in function, memory capacity and compactness havebeen requested, and, to achieve this, it is required that the degree ofthe integration of the integrated circuit be increased. In order toincrease the degree of the integration, individual circuit patternsshould be made smaller. However, a minimum pattern dimension of thecircuit is generally determined by performance of an exposure apparatusused in a circuit manufacturing process.

In an exposure apparatus utilizing photo-lithography, a circuit patternexactly described on a photo-mask is optically projected andtransferred, with reduced scale, onto a semiconductor wafer on whichphotoresist is coated. A minimum pattern size (resolving power) R on thewafer in the exposure is represented by the following equation (1) andthe depth of focus DF is represented by the following equation (2) whenit is assumed that a wavelength of a light source used for projection inthe exposure apparatus is λ and a numerical aperture of a projectionoptical system is NA:

R=K·λ/NA  (1)

DF=λ/{2·(NA)²}  (2)

where, K is a constant.

As apparent from the above equation (1), in order to decrease theminimum pattern size R, the constant K may be decreased or the numericalaperture NA may be increased or the wavelength λ may be decreased.

Here, the constant K is a constant determined by the projection opticalsystem or process and normally has a value of about 0.5 to 0.8. A methodfor decreasing the constant K is referred to as a super-resolutiontechnique in a broader sense.

Regarding such a technique, an improvement in the projection opticalsystem, modified illumination and a phase shift mask method have beenproposed and investigated. However, they had disadvantage thatapplicable patterns were limited. On the other hand, from the aboveequation (1), the greater the numerical aperture NA the smaller theminimum pattern size R. However, this also means that the depth of focusis decreased, as apparent from the above equation (2). Thus, there is alimit to increase the numerical aperture NA, and, in consideration ofthe balance between NA and DF, the value of the numerical aperture NA isnormally selected to about 0.5 to 0.6.

Accordingly, a most simple and effective method for decreasing theminimum pattern size is a method for decreasing the wavelength λ used inthe exposure. There are several conditions in achieving reduction of thewavelength and in manufacturing the light source of the exposureapparatus. Now, these conditions will be described.

In a first condition, light output of several watts is required forshortening a time period for exposing and transferring the integratedcircuit pattern.

In a second condition, in case of ultraviolet light having a wavelengthsmaller than 300 nm, material used for forming a lens of the exposureapparatus is limited, and it is difficult to correct chromaticaberration. Thus, monochromaticity of the light source is required andspectral width of must be smaller than 1 pm.

In a third condition, as spectral width is made narrower, temporalcoherence is increased. Therefore, if light having a narrow line widthis emitted as it is, an undesired interference pattern called as specklewill be generated. Accordingly, in order to suppress occurrence of thespeckle, the spatial coherence in the light source must be reduced.

In order to satisfy these conditions and to realize high resolvingpower, many attempts for decreasing the wavelength of the exposure lightsource have been made. Heretofore, reduction of the wave length has beeninvestigated mainly in the following two ways. One way is a developmentto apply an excimer laser having a short oscillation wavelength to theexposure apparatus, and the other way is a development of a shortwavelength exposure light source utilizing harmonic wave generation froman infrared or visual laser.

Among them, as the short wavelength light source realized by using theformer way, a KrF excimer laser (wavelength of 248 nm) is known, and,nowadays, an exposure apparatus using an ArF excimer laser (wavelengthof 193 nm) as a shorter wavelength light source is being developed.However, these excimer lasers have several disadvantages that they arebulky, that optical parts are apt to be damaged because of great energyper one pulse and that maintenance of the laser is troublesome andexpensive because of usage of harmful fluorogas.

On the other hand, as the latter way, there is a method for convertinglong wavelength light (infrared light or visual light) into shorterwavelength ultraviolet light by utilizing secondary non-linear opticaleffect of non-linear optical crystal. For example, in the document“Longitudinally diode pumped continuous wave 3.5 W green laser” (L. Y.Liu, M. Oka, W. Wiechmann and S. Kubota, Optic Letters, vol. 19 (1994),p 189), a laser light source for wavelength-converting light from asolid-state laser of semiconductor excitation type is disclosed. In thisconventional example, a laser beam having a wavelength of 1064 nm andemitted from an Nd:YAG laser is wavelength-converted by using thenon-linear optical crystal to thereby generate 4th harmonic light havinga wavelength of 266 nm. Further, the “solid-state laser” is a generalterm of lasers in which a laser medium is solid. Accordingly, although asemiconductor laser is included in the solid-state laser in a broadsense, normally, the solid-state laser means lasers excited by lightsuch as a Nd:YAG laser and a ruby laser, and, thus, in thisspecification, such a definition is used.

Further, as an example that the solid-state laser is used as the lightsource of the exposure apparatus, an array laser in which a plurality oflaser elements each comprising a laser generating portion for generatinga laser beam and a wavelength converting portion forwavelength-converting the light from the laser generating portion intoultraviolet light are bundled in a matrix patterns has been proposed.For example, Japanese Patent Laid-open No. 8-334803 (1996) discloses anexample of an array laser in which a plurality of laser elements forwavelength-converting light from a laser generating portion having asemiconductor laser into ultraviolet light by using non-linear opticalcrystal provided in a wavelength converting portion are bundled in amatrix pattern (for example, 10×10) to thereby form a single ultravioletlight source.

According to the array laser having the above-mentioned arrangement, bybundling the plurality of independent laser elements together, lightoutput of the entire apparatus can be increased while keeping lightoutput of the individual laser element at a lower level. Thus, the loadto the non-linear optical element can be reduced. However, since thelaser elements are independent, when they are applied to the exposureapparatus, as a whole, oscillation spectra of the laser elements must becoincided. For example, even when the line width of the oscillationspectrum of each laser elements is smaller than 1 pm, the difference inrelative wavelength in the entire assembly including the plural laserelements must not be 3 pm, and the entire width must be smaller than 1pm.

To achieve this, for example, lengths of resonators of the laserelements must be adjusted or wavelength selecting elements must beinserted into the resonators so that the laser elements each canindependently perform single longitudinal mode oscillation having thesame wavelength. However, these methods have disadvantages that theadjustment is delicate and that, as the number of laser elements isincreased, the arrangement for causing all of the laser elements toperform oscillation having the same wavelength becomes more complicated.

On the other hand, as a method for actively equalizing the wavelengthsfrom the plurality of laser elements, an injection seed method is wellknown (for example, refer to a document “Solid-state Laser Engineering”,3rd Edition, Springer Series in Optical Science, Vol. 1,Springer-Verlag, ISBN 0-387-53756-2, p 246-249 presented by WalterKoechner). This method is a technique in which light from a single laserlight source having narrow oscillation spectrum line width is branchedto a plurality of laser elements and oscillation wavelengths of thelaser elements coincide or are tuned by using the laser beams as seedlight, thereby making the line widths of the spectra narrower. However,this method has a disadvantage that the arrangement becomes complicated,since an optical path for branching the seed light into the laserelements and a tuning and controlling portion for the oscillationwavelengths are required.

Further, although such an array laser can make the entire apparatussmaller considerably in comparison with the conventional excimer lasers,it is still difficult to obtain a packaging capable of suppressingoutput beam diameter of the entire array to less than severalcentimeters. Further, in the array laser having such an arrangement,there arise problems that the laser is expensive because the wavelengthconverting portions are required for the respective arrays and that, ifmis-alignment occurs between the laser elements constituting the arrayor if the optical element(s) are damaged, in order to adjust the laserelements, the entire array must once be disassembled to remove the laserelements and the removed array must be assembled again after adjustmentthereof.

SUMMARY OF THE INVENTION

The present invention aims to eliminate the above-mentioneddisadvantages and problems, for example, problems regarding bulkiness ofthe apparatus, usage of harmful fluorogas and troublesome and expensivemaintenance which are caused when the excimer laser is used as theultraviolet light source of the exposure apparatus, problems regardingthe damage of the non-linear optical crystal and the occurrence of thespeckle due to increase in the spacial coherence which are caused whenthe harmonic wave of the solid-state laser such as the Nd:YAG laser isused as the ultraviolet light source of the exposure apparatus, andproblems regarding the complexity of the construction including thewavelength-coincidence mechanism, the difficulty in reduction ofdiameter of the output beam and the troublesome maintenance which arecaused when the array laser in which the plurality of laser elements forgenerating the ultraviolet light are bundled in the matrix pattern isused as the ultraviolet light source of the exposure apparatus.

Accordingly, an object of the present invention is to provide anultraviolet laser apparatus in which ultraviolet light having a singlewavelength and sufficiently narrower bandwidth for a light source of anexposure apparatus can stably be obtained as ultraviolet output lighthaving low spatial coherence and which is compact and easily handlable.

Another object of the present invention is to provide an exposureapparatus which is compact and has high degree of freedom and in whichsuch an ultraviolet laser apparatus which is compact and easilyhandlable is used as a light source.

The above object is achieved by an ultraviolet laser apparatuscomprising a laser generating portion for generating light having asingle wavelength, at least one stage optical amplifier having a fiberoptical amplifier for amplifying the generated laser light, and awavelength converting portion for wavelength-converting the lightamplified by the optical amplifier into ultraviolet light by using anon-linear optical crystal.

More specifically, the laser generating portion includes asingle-wavelength oscillating laser (for example, a DFB semiconductorlaser 31 in an embodiment and the like) having a narrow band, and thelaser light having the single wavelength is amplified by the fiberoptical amplifier (for example, an erbium doped fiber optical amplifiers33, 34 in an embodiment and the like), and the output light from thefiber amplifier is converted into an ultraviolet light (for example,ultraviolet light having a wavelength of 193 nm or 157 nm) by thewavelength converting portion using the non-linear optical crystal (forexample, crystals 502 to 504 in an embodiment and the like). In thisway, an ultraviolet laser apparatus which is compact and easilyhandlable and which is adapted to generate ultraviolet light having asingle wavelength and which constitutes the object of the invention isprovided.

Further, in the present invention, the output from the single-wavelengthoscillating laser (for example, DFB semiconductor lasers 11,21 or afiber laser in an embodiment and the like) is divided or branched by alight dividing or branching device. The output is divided into pluraloutputs by the light dividing or branching device (for example,splitters 14, 16 in an embodiment and the like), and the fibers arearranged behind the device, and, by bundling the plurality of fibers,the ultraviolet laser apparatus is formed. Further, the light dividingor branching device may have any design so long as the laser lightgenerated by the single-wavelength laser can be divided or branched inparallel.

By providing a device for preventing the branched light beams to beoverlapped in view of time, independent light beams can be obtained. Apreferred device for achieving this may comprise beam splitters forbranching the laser light generated by the single-wavelength laser intoplural light beams in parallel, and fibers having different lengths anddisposed at output sides of the beam splitters. In a preferred form ofthe fibers having different lengths, the lengths of the fibers areselected so that, after the laser beams branched in parallel passthrough the respective fibers, delay distances or intervals between thesuccessive laser beams becomes substantially the same at the output endsof the fibers.

Further, according to one aspect of the present invention, as the lightdividing or branching device, a time division multiplexer (TDM) (forexample, a TDM 23 in an embodiment) for distributing the light intorespective light paths every predetermined time is used.

Next, as the plurality of fibers disposed on the output sides of thelight dividing or branching device, a plurality of fiber opticalamplifiers are preferable. Further, it is preferable that the lightbeams are amplified by the fiber optical amplifiers (for example, erbiumdoped fiber optical amplifiers or ytterbium doped fiber opticalamplifiers 18, 19 in an embodiment and the like) and the plurality offiber optical amplifiers are bundled. With this arrangement, laser lighthaving higher intensity can be obtained. Further, if necessary,non-doped fibers may be coupled to the output ends (for example, fiberoutput ends 114, 29 in an embodiment and the like) of the plurality offiber optical amplifiers.

In the fiber output ends, it is preferable that diameters of cores (forexample, a core 421 in the drawing of an embodiment) of the fibers aregently diverged in a tapered fashion toward the output end faces.Further, it is preferable that a window member (for example, windowmembers 433, 443 in an embodiment and the like) which are transparent tothe laser light is provided on the fiber output ends. With thisarrangement, power density (light intensity per unit area) of the laserlight can be reduced at the fiber output ends, and, accordingly, thefiber output ends can be prevented from being damaged.

Further, according to the present invention, in a plurality of fibersprovided on an incident side of the wavelength converting portion, it ispreferable that output ends of the fibers are bundled as a single bundleor plural bundles and are formed as a single output group or pluraloutput groups (for example, bundle outputs 114, 29, 501, 601, 701 in anembodiment and the like) to match with the construction of thewavelength converting portion. And, in the wavelength convertingportion, harmonic wave generation for fundamental wave is effected byone set or plural sets of non-linear optical crystals (for example,crystals 502 to 504 in a fourth embodiment or crystals 842 to 844 in aneighth embodiment) to output ultraviolet light (for example, ultravioletlight having a wavelength of 193 nm or 157 nm). By providing one set ofwavelength converting portions, the apparatus can be made more compactand cheaper, and, by providing the plural sets of wavelength convertingportions, since the load acting on each set can be reduced, high outputcan be achieved as a whole.

Further, when the optical amplifier is constituted by the plurality offiber optical amplifiers, in order to suppress fluctuation inultraviolet light outputs due to fluctuation in amplification gain ofthe fiber optical amplifiers, it is desirable to provide a fiber outputcontrol device for monitoring the output lights from the fibers tocontrol pumping power of the fiber optical amplifiers. Further, in orderto equalize light wavelengths of the ultraviolet light outputs to aspecific wavelength, it is desirable to provide a control device forcontrolling the oscillating wavelength of the single wavelengthoscillating laser by using the frequency of fundamental wave or theharmonic wave in the wavelength converting portion.

Light collecting optical elements are provided at the incident sides ofthe wavelength converting portions. Application of the light collectingoptical elements can be appropriately selected in accordance with theoutput conditions of the optical amplifiers. For example, according toone aspect, the light collecting optical elements (for example, lenses902, 453 in an embodiment and the like) may be provided for each fiberoutput, or, according to another aspect, the light collecting opticalelements (for example, lenses 845,855,463 in an embodiment and the like)may be provided for each of the bundled output groups.

By the way, as an arrangement for outputting the ultraviolet light, forexample, there is a technique in which a laser beam having a wavelengthof about 1.5 μm is emitted from the laser light generating portion, and,regarding the optical amplifier, at least one stage optical amplifierhaving the fiber optical amplifiers for amplifying the fundamental wavehaving a wavelength of about 1.5 μm is provided, and, a wavelengthconverting portion for effecting 8th harmonic wave generation for theamplified fundamental wave is also provided. With this arrangement, theultraviolet light having output wavelength of about 190 nm can begenerated. The output light can be made to have the same wavelength asthe wavelength (of 193 nm) of the ArF excimer laser by tuning theoscillating wavelength of the laser light generating portion more finely(for example, 1.544 to 1.522 μm).

Further, as another arrangement for outputting the ultraviolet light,for example, there is a technique in which, similar to theabove-mentioned arrangement, a laser beam having a wavelength of about1.5 μm is emitted from the laser light generating portion, and,regarding the optical amplifier, at least one stage optical amplifierhaving the fiber optical amplifiers for amplifying the fundamental wavehaving a wavelength of about 1.5 μm is provided, and, a wavelengthconverting portion for effecting 10th harmonic wave generation for theamplified fundamental wave is also provided. With this arrangement, theultraviolet light having output wavelength of about 150 nm can begenerated. This output light can be made to have the same wavelength asthe wavelength (of 157 nm) of the F₂ laser by tuning the oscillatingwavelength of the laser light generating portion more finely (forexample, 1.57 to 1.58 μm).

Further, as a further arrangement for outputting the ultraviolet light,for example, there is a technique in which a laser beam having awavelength of about 1.1 μm is emitted from the laser light generatingportion, and, regarding the optical amplifier, at least one stageoptical amplifier having the fiber optical amplifiers for amplifying thefundamental wave having a wavelength of about 1.1 μm is provided, and, awavelength converting portion for effecting 7th harmonic wave generationfor the amplified fundamental wave is also provided. With thisarrangement, the ultraviolet light having output wavelength of about 150nm can be generated. The output light can be made to have the samewavelength as the wavelength (of 157 nm) of the F₂ laser by tuning theoscillating wavelength of the laser light generating portion more finely(for example, 1.099 to 1.106 μm).

Further, as the other arrangement for outputting the ultraviolet light,for example, by providing a laser light generating portion including asemiconductor laser or a fiber laser having oscillating wavelength ofabout 990 nm, at least one stage optical amplifier having the fiberoptical amplifiers for amplifying the fundamental wave having awavelength of about 990 nm, and a wavelength converting portion foreffecting 4th harmonic wave generation for the amplified fundamentalwave, the ultraviolet light having the same wavelength as the wavelength(of 248 nm) of the KrF excimer laser can be obtained.

The wavelength converting portion for effecting such a harmonic wavegeneration can be designed as various arrangements as will be describedin embodiments of the present invention which will be described later.For example, briefly explaining an example of an arrangement of thewavelength converting portion for effecting 8th harmonic wave generationfor the fundamental wave, such an arrangement can be constituted by athree-stage harmonic wave generation light path system (for example,FIG. 11(a) in a fourth embodiment) for converting the fundamental waveinto 2nd harmonic wave→4th harmonic wave→8th harmonic wave by utilizingsecond harmonic wave generation (SHG) of the non-linear optical crystalin all of the wavelength converting stages. With this arrangement, adesired 8th harmonic wave can be obtained with least number of stages.

Further, as another preferred arrangement for obtaining the 8th harmonicwave, there is an arrangement (for example, FIG. 11(d) in a fourthembodiment and the like) in which 3rd harmonic wave and 4th harmonicwave of the fundamental wave are generated by also utilizing sumfrequency generation (SFG) of the non-linear optical crystal in thewavelength converting stages, and these waves are subjected to sumfrequency generation to generate 7th harmonic wave of the fundamentalwave, and further, the 7th harmonic wave and the fundamental wave aresubjected to sum frequency generation to generate 8th harmonic wave ofthe fundamental wave. In this arrangement, a LBO crystal having lowabsorption coefficient for ultraviolet light having the wavelength of193 nm can be used for 8th harmonic wave generation in the last stage.Further, regarding 7th harmonic wave generation and 10th harmonic wavegeneration from the fundamental wave, similar to 8th harmonic wavegeneration from the fundamental wave, the second harmonic wavegeneration and the sum frequency generation of the non-linear opticalcrystal can be used.

Further, according to an aspect of the present invention, ultravioletpulse laser light can be obtained by providing a pulsing device (forexample, light modulating elements 12, 22 in an embodiment and the like)for pulsing CW laser light of the single wavelength oscillating laser inthe laser generating portion or by pulse-oscillating the singlewavelength oscillating laser or by doing both. Further, by using theultraviolet laser apparatus having the above-arrangement as a lightsource of a projection exposure apparatus, and by providing anillumination optical system for illuminating light from the light sourceonto a mask on which a projection pattern is printed with substantiallyuniform intensity and a projection objective optical system forprojecting the pattern printed on the mask onto a wafer, a projectionexposure apparatus having easy maintenance can be obtained.

EFFECT OF THE INVENTION

As mentioned above, according to the present invention, since the lighthaving single wavelength from the laser generating portion is amplifiedby the optical amplifier in the light source and the amplified light isconverted into the ultraviolet light by the non-linear optical crystalof the wavelength converting portion, the ultraviolet light having thedesired spectrum line width (for example, 1 pm or less) can easily beobtained without complicated arrangement.

Further, since the laser light having single wavelength is divided (ormultiplexed) into the plurality of output lights and the plural outputlights are amplified by the plurality of fiber optical amplifiers andthe amplified lights are converted into the ultraviolet lights by thenon-linear optical crystals, the entire laser light output can beincreased while suppressing the peak power of the pulse light per onepulse and the ultraviolet light having low spatial coherence can beobtained.

That is to say, according to the present invention, there can beprovided an ultraviolet laser apparatus which is compact and has highdegree of freedom regarding arrangement of parts and in which themaintenance is easy and the non-linear optical crystal is hard to bedamaged and the spatial coherence is low.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing an arrangement of a laser lightgenerating portion and an optical amplifier of an ultraviolet laserapparatus according to a first embodiment of the present invention;

FIG. 2 is an explanatory view showing an arrangement of a laser lightgenerating portion and an optical amplifier of an ultraviolet laserapparatus according to a second embodiment of the present invention;

FIG. 3 is an explanatory view showing an arrangement of a laser lightgenerating portion and an optical amplifier of an ultraviolet laserapparatus according to a third embodiment of the present invention;

FIG. 4 is an explanatory view showing an arrangement of an opticalamplifier according to another embodiment of the present invention;

FIG. 5 is a sectional view of a double clad fiber;

FIG. 6 is a graph showing a relationship between a wavelength and gainregarding elements doped in an erbium doped fiber optical amplifier;

FIG. 7 is a graph showing change in gain with respect to pumping powerin a fiber optical amplifier in which erbium and ytterbium are co-doped;

FIG. 8 is a constructional view showing an arrangement of a fiber outputcontrol device of the ultraviolet laser apparatus according to thepresent invention;

FIG. 9 is an enlarged side view of a fiber core at an output end of thefiber optical amplifier;

FIG. 10(a) is a side view showing an example of the output end of thefiber optical amplifier, and

FIG. 10(b) is a side view showing another example of the output end ofthe fiber optical amplifier;

FIGS. 11(a) to 11(d) are explanatory views showing first to fourthexamples of an arrangement of a wavelength converting portion of anultraviolet laser apparatus according to a fourth embodiment of thepresent invention;

FIGS. 12(a) to 12(d) are views showing tables corresponding the first tofourth examples of FIGS. 11(a) to 11(d) and each indicating conversionefficiency of the wavelength converting portion;

FIG. 13 is an explanatory view showing an arrangement of a wavelengthconverting portion of an ultraviolet laser apparatus according to afifth embodiment of the present invention;

FIG. 14 is an explanatory view showing an arrangement of a wavelengthconverting portion of an ultraviolet laser apparatus according to asixth embodiment of the present invention;

FIG. 15 is an explanatory view showing an arrangement of a wavelengthconverting portion of an ultraviolet laser apparatus according to aseventh embodiment of the present invention;

FIG. 16 is an explanatory view showing an example of an input part of awavelength converting portion of an ultraviolet laser apparatusaccording to an eighth embodiment of the present invention;

FIG. 17 is an explanatory view showing another embodiment of an inputpart of the wavelength converting portion of the ultraviolet laserapparatus according to the present invention;

FIGS. 18(a) to 18(c) are explanatory views showing first to thirdexamples of a further embodiment of an input part of the wavelengthconverting portion of the ultraviolet laser apparatus according to thepresent invention;

FIG. 19 is an explanatory view showing an exposure apparatus accordingto another embodiment of the present invention; and

FIG. 20 is an explanatory view showing an exposure apparatus accordingto a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be explained in connection withembodiments thereof with reference to the accompanying drawings.

First of all, an ultraviolet laser apparatus according to a firstembodiment of the present invention will be described with reference toFIG. 1. An ultraviolet light generating apparatus according to the firstembodiment comprises a laser light generating portion including a singlewavelength oscillating laser 11 and adapted to generate a laser beam (orlight) having a single wavelength, an optical amplifier including fiberoptical amplifiers 13, 18 and 19 and adapted to amplify the light, lightbranching devices 14, 16 for branching the light into plural parallelbeams, fibers 15, 17 having different lengths, and a wavelengthconverting portion including a non-linear optical crystal (describedlater) and adapted to wavelength-convert the amplified light, therebyproviding an ultraviolet light generating apparatus capable ofgenerating output wavelength same as output wavelength (193 nm) of anArF excimer laser or output wavelength (157 nm) of an F₂ laser with lowspatial coherence.

In the illustrated embodiment, FIG. 1 shows an example of an arrangementin which the laser light having the single wavelength is outputted fromthe laser generating portion of the ultraviolet laser apparatusaccording to the present invention and is branched and amplified. Firstof all, explaining with reference to FIG. 1, the laser generatingportion includes the single wavelength oscillating laser 11 forgenerating the laser beam having a single wavelength, and further, thereare provided splitters (light branching devices) 14, 16 and the fibers15, 17 having different lengths, and fiber optical amplifiers 18, 19 areconnected to output ends of the fibers 17 having different lengths sothat the plural light beams are amplified in parallel. Output ends ofthe fiber optical amplifiers 19 are bundled so that the amplified laserbeams are incident on a wavelength converting portion (502 to 506) asshown in FIG. 11(a), for example. A fiber bundle output end 114 of thefiber optical amplifiers corresponds to fiber bundle output ends 501shown in FIGS. 11(a) to 11(d), respectively. The wavelength convertingportion includes non-linear optical crystals 502 to 504 so that thefundamental wave emitted from the fiber optical amplifier 19 isconverted into ultraviolet light. The wavelength converting portionaccording to the present invention will be fully described later withreference to fourth to seventh embodiments.

Now, the first embodiment will be fully explained. As the singlewavelength oscillating laser 11 for generating the laser beam having asingle wavelength, for example, InGaAsP, DFB semiconductor laser havingan oscillating wavelength of 1.544 μm and continuous wave output(referred to as “CW output” hereinafter) of 20 mW. The DFB semiconductorlaser is designed so that, in place of a Fabry-Perot resonator havinglow longitudinal mode selection, diffraction gratings are incorporatedinto a semiconductor laser to perform single longitudinal modeoscillation under any conditions and is called as a distributed feedback(DFB) laser. In such a laser, since single longitudinal mode oscillationis effected fundamentally, a line width of an oscillation spectrum canbe suppressed below 0.01 pm.

Further, in order to fix the output wavelength of the ultraviolet laserapparatus to a given wavelength, it is preferable to provide anoscillating wavelength controlling device for controlling theoscillating wavelength of the single wavelength oscillating laser(master oscillator) to become the given wavelength. Alternatively, it isalso preferable that the oscillating wavelength of the single wavelengthoscillating laser is positively changed by the oscillating wavelengthcontrolling device to permit adjustment of output wavelength thereof.For example, when the laser apparatus according to the present inventionis applied to an exposure apparatus, according to the former, occurrenceor fluctuation of aberration of a projection optical system due towavelength fluctuation is prevented, thereby preventing change inimaging characteristics (optical characteristics such as image quality)during pattern transferring. On the other hand, according to the latter,fluctuation in focusing property (aberration and the like) of theprojection optical system caused in accordance with differences inheight level, atmospheric pressure and environment (atmosphere in aclean room) between a manufacturing place where the exposure apparatusis assembled and adjusted and a setting place where the exposureapparatus is installed can be cancelled so that the time for preparingthe exposure apparatus in the setting place can be reduced. Further,according to the latter, during the operation of the exposure apparatus,fluctuation in aberration, projection magnification and focusingposition of the projection optical system caused due to change inillumination of exposure illumination light and atmospheric pressure canalso be cancelled, so that a pattern image can always be transferredonto a substrate under a best focusing condition.

In such an oscillating wavelength controlling device, for example, theDFB semiconductor laser is used as the single wavelength oscillatinglaser, the given wavelength can be achieved by controlling a temperatureof the DFB semiconductor laser, and, thus, by this method, theoscillating wavelength can be further stabilized to control it to becomethe given wavelength or to finely adjust the output wavelength.

Normally, the DFB semiconductor laser is provided on a heat sink and iscontained in a frame together with the heat sink. Thus, in theillustrated embodiment, a temperature adjuster (for example, Peltierelement) provided on the heat sink added to the single wavelengthoscillating laser (such as the DFB semiconductor laser) 11 is used tocontrol the temperature, thereby adjusting the oscillating wavelength.In the DFB semiconductor laser, the temperature can be adjusted with aunit of 0.001° C. Further, oscillating wavelength of the DFBsemiconductor laser has temperature dependency of about 0.1 nm/° C. Forexample, in the fundamental wave (1544 nm), since the wavelength ischanged by 0.1 nm when the temperature of the DFB semiconductor laser ischanged by 1° C., a wavelength of 8th harmonic wave (193 nm) is changedby 0.0125 nm and a wavelength of 10th harmonic wave (157 nm) is changedby 0.01 nm. Further, in the exposure apparatus, it is sufficient thatwavelength of the exposure illumination light (pulse light) can bechanged by about ±20 pm with respect to the center wavelength.Accordingly, the temperature of the DFB semiconductor laser may bechanged by about ±1.6° C. for the 8th harmonic wave and by about ±2° C.for the 10th harmonic wave.

As a monitor wavelength of feedback control when the oscillatingwavelength is controlled to become the given wavelength, among theoscillating wavelength of the DFB semiconductor laser and wavelengthconversion outputs (described later) (2nd harmonic wave, 3rd harmonicwave, 4th harmonic wave and the like), a wavelength which can providerequired sensitivity in the desired wavelength control and which iseasily monitored is selected. For example, when the DFB semiconductorlaser having the oscillating wavelength of 1.51 to 1.59 nm is used asthe single wavelength oscillating laser, 3rd harmonic wave of theoscillating laser light becomes a wavelength of 503 to 530 nm, and thisspectral bandwidth corresponds to a spectral bandwidth in whichabsorption lines of iodine molecules exist densely. Thus, by selectingproper iodine molecule absorption line to lock it to become the targetwavelength, exact oscillating wavelength control can be effected.

The light output (CW light) of the semiconductor laser 11 is convertedinto pulse light, for example, by using a light modulating element 12such as an electro-optical light modulating element or anacousto-optical light modulating element. In the illustrated embodiment,as an example, a case where the output is modulated to pulse lighthaving pulse width of 1 ns and-repetition frequency of 100 kHz (pulseperiod of 10 μs) will be explained. As a result of such lightmodulation, a peak power of the pulse light outputted from the lightmodulating element 12 becomes 20 mW and an average output becomes 2 μW.Here, while an example that there is no loss due to insertion of thelight modulating element 12 was explained, if there is insertion loss,for example, if insertion loss is −3 dB, the peak power of the pulselight will be 10 mW and the average output will be 1 μW.

Further, when the electro-optical light modulating element is used asthe light modulating element, it is preferable to use an electro-opticallight modulating element (for example, two electrode type modulator)having an electrode structure chirp-corrected to reduce wavelengthexpansion of the output of the semiconductor laser due to chirpassociated with the time change in refractive index. Further, by settingthe repetition frequency to more than about 100 kHz, reduction inamplification degree due to influence of ASE (amplified spontaneousemission) noise in the fiber optical amplifier which will be describedlater can be prevented. Such an arrangement of the modulator isdesirable.

Further, the output light can be pulse-oscillated by controlling thecurrent of the semiconductor laser. Thus, in the illustrated embodiment(and other embodiments which will be described later), it is preferablethat the pulse light is generated both by using the current control ofthe single wavelength oscillating laser (DFB semiconductor laser) 11 andby using the light modulating element 12. In this way, for example,pulse light having a pulse width of about 10 to 20 ns is oscillated bycontrolling the current of the DFB semiconductor laser 11 and only apart of the pulse light is picked up by the light modulating element 12.That is to say, in the illustrated embodiment, the light is modulated tothe pulse light having a pulse width of 1 ns. By doing so, in comparisonwith the case where only the light modulating element 12 is used, pulselight having narrower pulse width can easily be generated and anoscillation interval, and timing of oscillation start and stop of thepulse light can easily be controlled. Particularly, when the oscillationof the pulse light is going to be stopped by using only the lightmodulating element 12, if a part thereof is outputted, it is desirablethat the current control of the DFB semiconductor laser is also effectedsimultaneously. The pulse light output obtained in this way is coupledto a first stage erbium (Er) doped fiber optical amplifier (EDFA) 13,thereby effecting light amplification of 35 dB (3162 times). In thiscase, the pulse light has a peak power of about 63 W and an averageoutput of about 6.3 mW.

Output of the fiber amplifier (first stage optical amplifier) 13 isfirstly divided in parallel into four outputs of channels 0 to 3 by thesplitter (flat plate waveguide 1×4 splitters) 14 as the light dividingdevice. By coupling the outputs of the channels 0 to 3 to the fibers 15having different lengths (only one fiber for the channel 0 isillustrated), the lights outputted from the fibers are time-delayed inaccordance with the lengths of the fibers. In the illustratedembodiment, for example, it is assumed that the propagating speed of thelight through the fiber is 2×10⁸ m/s, and the fibers having the lengthsof 0.1 m, 19.3 m, 38.5 m and 57.7 m, respectively are connected to thechannels 0, 1, 2 and 3, respectively. In this case, the delay of lightbetween the adjacent channels at the outlets of the fibers becomes 96ns. Further, here, the fiber used for delaying the light is referred toas “delay fiber”.

Then, outputs of four delay fibers are further divided into 32 outputsin parallel by the splitter 16 (flat plate waveguide 1×32 splitters) of4 block type (channels 0 to 31 in each block), i.e., divided into 128channels in total. Further, fibers having different lengths areconnected to the channels 1 to 31 of each block (except for the channel0). In the illustrated embodiment, for example, the fibers havinglengths of 0.6×N meters (N: channel number) are connected to thechannels 1 to 31, respectively. As a result, the delay of 3 ns is givenbetween the adjacent channels in each block, so that the delay of theoutput of the channel 31 with respect to the output of the channel 0 ineach block becomes 93 ns (=3×31).

On the other hand, between the adjacent blocks of the first to fourthblocks, as mentioned above, the delay of 96 ns is given by the delayfibers 15 at the entrance of the block. Accordingly, the output of thechannel 0 of the second block is delayed by 96 ns with respect to theoutput of the channel 0 of the first block and is delayed by 3 ns withrespect to the output of the channel 31 of the first block. The same istrue between the second and third blocks and between the third andfourth blocks. As a result, as the entire output, at output ends of 128channels (in total), pulse lights having delay of 3 ns between theadjacent channels can be obtained. Further, in FIG. 1, although only thechannels of the first block are illustrated and the other channels areomitted, the same is true with respect to the other channels.

By the above-mentioned branching and delaying, at the output ends of 128channels (in total), the pulse lights having delay of 3 ns between theadjacent channels can be obtained. In this case, the light pulseobserved at each output end is 100 kHz (pulse period: 10 μs) which isthe same as that of the pulse modulated by the light modulating element12. Accordingly, in consideration of the entire laser light generatingportion, after 128 pulses are generated with interval or period of 3 ns,next pulse group is generated after a period of 9.62 μs. Such generationis repeated with 100 kHz. That is to say, the entire output becomes128×100×10³=1.28×10⁷ pulses/sec.

Further, in the illustrated embodiment, while an example that the numberof divisions is 128 and short delay fibers are used was explained. Thus,a non-light emitting interval of 9.62 μs is generated between the pulsegroups. However, the periods between the pulses can be completelyequidistant by increasing the number of divisions or by increasing thelengths of the delay fibers to have proper values or by usingcombination thereof. For example, the equidistant periods can beachieved by selecting the lengths of the fibers so that the delayintervals between the fibers become 1/(f×m) when it is assumed that thepulse repetition frequency of the laser beam incident on the splitter 14is f [Hz] and the number of divisions is m. Further, the number ofdivisions of at least one of the splitters 14, 16 or the pulserepetition frequency f defined by the light modulating elements 12 orboth may be adjusted to obtain the complete equidistant pulse intervals.Accordingly, by adjusting the fiber lengths of the delay fibers 15, 17and/or division number of at least one of the splitters 14, 16 and/orthe pulse repetition frequency f, not only the pulse intervals can bemade equidistant, but also the pulse intervals can be set at desiredones.

Further, in order to alter the fiber lengths after the light source wasassembled, for example, it is preferable that the delay fibers 15, 17are bundled as a unit and such a unit can be exchanged by another delayfiber unit having different delay time between channels. Further, alsowhen the division numbers of the splitters 14, 16 are to be altered, itis preferable that other splitters having different division numbers areprepared in correspondence to the splitters 14, 16 to permit theexchange between the splitters. In this case, it is desirable that thedelay fiber unit can be exchanged by another unit when the divisionnumbers of the splitters 14, 16 are altered.

Further, in the illustrated embodiment, by controlling a timing of drivevoltage pulses applied to the light modulating element 12, anoscillation timing of the light source (pulse light), i.e., therepetition frequency f (pulse period) can be adjusted. Further, if theoutput of the pulse light may be changed as the oscillation timing isaltered, the magnitude of the drive voltage pulse applied to the lightmodulating element 12 may be simultaneously adjusted to compensate forthe fluctuation of output. In this case, the fluctuation of output ofthe pulse light may be compensated by effecting only the oscillationcontrol of the single wavelength oscillating laser 11 or through acombination of such an oscillation control and the control of the lightmodulating element 12. Further, the fluctuation of output of the pulselight may be generated not only when the oscillating timing is alteredbut also when the oscillation of the single wavelength oscillating laser(i.e., input of the pulse light to the fiber optical amplifiers) isre-started after such an oscillation was stopped for a predeterminedtime period. Further, when the single wavelength oscillating laser 11 ispulsated, the oscillation timing (pulse period) of the pulse light maybe adjusted by only the current control of the single wavelengthoscillating laser 11 or by the combination of such a current control andthe control of the light modulating element 12.

In the illustrated embodiment, the fiber optical amplifiers 18 areconnected to 128 (in number) delay fibers 17, and the fiber opticalamplifiers 19 are connected to the fiber optical amplifiers 18 with theinterposition of a narrow band filter 113. The narrow band filter 113serves to make the spectral bandwidth of transmitted (or permeated)light narrower by cutting the ASE lights generated in the fiber opticalamplifiers 13, 18 and by permitting transmission (or permeation) ofoutput wavelength (having spectral bandwidth less than about 1 pm) ofthe DFB semiconductor laser 11. As a result, the ASE light can beprevented from entering the later stage fiber optical amplifiers (18,19), thereby preventing reduction of gain of the laser light. Althoughthe narrow band filter preferably permits transmission of wavelengthhaving a width of about 1 pm, since the spectral bandwidth of the ASElight is about several tens of nm, even when a narrow band filterpermitting transmission of wavelength having about 100 pm presentlyobtained is used, the ASE light can be cut without any substantialproblems. Further, when the output wavelength of the DFB semiconductorlaser 11 is desired to be positively altered, although the narrow bandfilter may be exchanged by another one in correspondence to new outputwavelength, it is preferable that a narrow band filter having atransmissible spectral bandwidth in correspondence to a variable width(as an example, about ±20 pm in the exposure apparatus) of the outputwavelength (i.e., same as the variable width or more) is used. Further,in the laser apparatus applied to the exposure apparatus, the spectralbandwidth thereof is set below about 1 pm. Further, the laser apparatusshown in FIG. 1 is provided with three isolators 110, 111, 112 so thatinfluence of return light can be reduced by these isolators.

With the arrangement as mentioned above, the output lights emitted fromthe generating portion (i.e., from the output ends of the fiber opticalamplifiers 19) are not overlapped with each other in view of timealthough they have narrow bands. Accordingly, the spatial coherencebetween the channel outputs can be reduced.

Further, in the above-mentioned arrangement, while an example that theDFB semiconductor laser is used as the single wavelength oscillatinglaser 11 and the splitters 14, 16 of flat plate waveguide type are usedas the branching elements of the light branching device was explained,any laser having narrow band at this wavelength region may be used asthe laser light source, similar to the DFB semiconductor laser. Forexample, an erbium (Er) doped fiber laser can achieve the same effect.Further, any element capable of branching the light in parallel may beused as the branching element of the light branching device, similar tothe splitter of flat plate waveguide type. For example, a fiber splitteror a beam splitter using partial light-transmissible mirror can achievethe same effect.

Further, as mentioned above, in the illustrated embodiment, the outputsof the fibers 17 (delay fibers) are further amplified by a single stageEDFA or a multi-stage EDFA (erbium doped fiber optical amplifiers, whichwill be referred to as “EDFA” hereinafter). In the illustratedembodiment, as an example, an example that an average output of about 50μW at each channel of the laser light generating portion, i.e., anaverage output of about 6.3 mW for the entire channels is amplified bytwo-stage EDFAs 18, 19 by 46 dB (40600 times) in total is shown. In thiscase, at the output end of each channel, the output light having a peakpower of 20 kW, pulse width of 1 ns, pulse repetition frequency of 100kHz and average output of 2 W (average output of about 256 W in theentire channels) can be obtained. Here, although coupling loss at thesplitters 14, 16 of flat plate waveguide type is not taken inconsideration, if there is such a coupling loss, by increasing the gainof the fiber optical amplifiers (for example, at least one of EDFAs 18,19) by an amount corresponding to the coupling loss, the output of thefundamental wave generated from the EDFA 19 can be made the same as theaforementioned value (for example, peak power of 20 kW and the like).Further, by changing the gain of the fiber optical amplifier, the outputof the fundamental wave can be increased or decreased with respect tothe aforementioned value.

The single wavelength pulse laser light having wavelength of 1.544 μm(output of the optical amplifier) is converted into an ultraviolet lightpulse output light having narrow spectrum line width by the wavelengthconverting portion using the non-linear optical crystals. The wavelengthconverting portion will be described later.

Next, a second embodiment of an ultraviolet laser apparatus according tothe present invention will be explained with reference to FIG. 2. Theultraviolet laser apparatus according to the second embodiment comprisesa laser light generating portion for generating a laser light having asingle wavelength, an optical amplifier for amplifying the light, and awavelength converting portion for wavelength-converting the amplifiedlight, thereby providing an ultraviolet light generating apparatuscapable of generating an output wavelength same as output wavelength(193 nm) of an ArF excimer laser or an output wavelength (157 nm) of anF₂ laser with low spatial coherence. Further, the ultraviolet laserapparatus according to the second embodiment differs from theultraviolet laser apparatus according to the first embodiment of thepresent invention in two points that the light branching device dividesand branches the light in view of time and that the laser light beforeincident on the light branching device is not amplified by the fiberoptical amplifiers. Thus, it is possible that the light branching devicemay be disposed ahead of the fiber optical amplifiers or vice versa.Further, similar to the first embodiment (FIG. 1), fiber opticalamplifiers may further be provided on an incident side (i.e., on a sideof a single wavelength oscillating laser 21) of the light branchingdevice (TDM 23 in this embodiment) so that the pulse light amplified inthe fiber optical amplifiers is incident on the light branching device.With this arrangement, required gain can be reduced by the fiber opticalamplifiers (24, 25 in the illustrated embodiment) disposed behind (laterstage) the light branching device in comparison with the arrangementshown in FIG. 2, with the result that, for example, since the number ofreplacing fiber optical amplifiers is reduced, a cheaper apparatus canbe realized.

By the way, in the second embodiment, FIG. 2 shows an example of anarrangement of laser light generating portion, light branching deviceand optical amplifier of the ultraviolet laser apparatus according tothe present invention. As shown in FIG. 2, the ultraviolet laserapparatus according to the second embodiment comprises the laser lightgenerating portion including a single wavelength oscillating laser 21for generating the laser beam having a single wavelength, and a lightbranching device 23 for branching the light, and plural light outputsfrom the light branching device 23 are amplified in parallel,respectively by fiber optical amplifiers 24, 25. Output ends of thefiber optical amplifiers 25 are bundled, so that the amplified laserlight is incident on a wavelength converting portion (702 to 712)comprised of non-linear optical crystals shown in FIG. 14, for example.Fiber bundle output ends 29 of the fiber optical amplifiers 25 shown inFIG. 2 correspond to fiber bundle output ends 701 shown in FIG. 14. Thiswavelength converting portion has a group of non-linear optical crystals702, 705, 710, 712 for converting the fundamental waves emitted fromoptical fibers (21 to 28) into ultraviolet lights. Further, thewavelength converting portion according to the present invention will befully described later with reference to fourth to seventh embodiments.

Now, the second embodiment will be fully described. As the singlewavelength oscillating laser 21 for generating the laser beam having asingle wavelength, for example, an ytterbium (Yb) doped fiber laser or aDFB semiconductor laser having an oscillating wavelength of 1.099 μm andCW output of 20 mW is used. In such lasers, since single longitudinalmode oscillation is effected fundamentally, a line width of anoscillation spectrum can be suppressed to less than 0.01 pm.

The light output (CW light) of this semiconductor laser is convertedinto pulse light, for example, by using a light modulating element 22such as an electro-optical light modulating element or anacousto-optical light modulating element. In the illustrated embodiment,as an example, a case where the output is modulated to pulse lighthaving pulse width of 1 ns and repetition frequency of 12.8 MHz (pulseperiod of 78 μs) will be explained. As a result of such lightmodulation, a peak power of the pulse light outputted from the lightmodulating element becomes 20 mW and average output becomes 0.256 mW.

The output of the pulse light is shared or branched into 128 channels(in total) from a channel 0 to a channel 127 successively for each pulseby means of a time division multiplexer (TDM) 23 which is the lightbranching device. That is to say, the pulses with pulse period of 78 nsare successively shared into the channels 0, 1, 2, 3, . . . 127.Observing the result for each channel, the pulse light having pulseperiod of 10 μs (=78 ns×128) (pulse frequency of 100 kHz), pulse peakpower of 20 mW and average output of 2 μW can be obtained. Further, inconsideration of the entire laser light generating portion, the averagedpulse light having pulse frequency of 12.8 MHz, pulse peak power of 20mW and average output of 0.256 mW can be obtained. Further, there is adelay of 78 ns between the adjacent channels, and, thus, the pulselights between the channels are not overlapped with each other. Further,in the illustrated embodiment, the repetition frequency f of the pulselight outputted from the light modulating element 12 is selected to 100kHz (pulse period of 10 μs) and the pulse lights outputted from thechannels 0 to 127 of the time division multiplexer (TDM) 23 are delayedby equidistant period or interval (78 ns) which is obtained by dividingthe pulse period (10 μs) defined by the light modulating element 22 by128. This delay interval may not be equidistant time interval or,similar to the aforementioned first embodiment, the pulse lights may beoutputted from the channels 0 to 127 at only a part of the pulse period(10 μs). Further, a timing of drive voltage pulse applied to the lightmodulating element 22 may simultaneously be controlled to alter thepulse period (10 μs), and, for example, the delay time obtained bydividing the pulse period by 128 can be altered.

Further, similar to the first embodiment, also in this embodiment, thesingle wavelength oscillating laser 12 may be pulsated. Alternatively,the pulse period (10 μs) may be altered by a combination of the controlof the time division multiplexer (TDM) 23 and the current control of thesingle wavelength oscillating laser 21 or a combination of such controlsand the control of the light modulating element 22.

With the arrangement as mentioned above, the output lights emitted fromthe generating portion are not overlapped with each other in view oftime while they are single wavelength lights and have narrow bands,respectively. Accordingly, the spatial coherence between the channeloutputs can be reduced.

Further, in the above-mentioned arrangement, while an example that theDFB semiconductor laser or the ytterbium (Yb) doped fiber laser is usedas the single wavelength oscillating laser 21 was explained, any laserhaving narrow band at this wavelength region may be used as the laserlight source to achieve the same effect, similar to the DFBsemiconductor laser.

The output of the time division multiplexer 23 is amplified by fiberoptical amplifiers 24, 25 comprised of single stage or multi-stage YDFAs(ytterbium doped fiber amplifiers; ytterbium doped fiber opticalamplifier will be referred to as “YDFA” hereinafter). The ytterbiumdoped fiber optical amplifier has a higher exciting efficiency than thatof the erbium doped fiber optical amplifier and thus is more economical.Further, similar to the first embodiment (FIG. 1), for the purpose ofreducing the influence of the return light and making the spectralbandwidth narrower, an isolator 26 is disposed between the singlewavelength oscillating laser 21 and the light modulating element 22, anda narrow band filter 28 and an isolator 27 are disposed between thefiber optical amplifiers 24 and the other fiber optical amplifiers 25.

In the illustrated embodiment, as an example, an example that an averageoutput of about 2 μW at each channel of the time division multiplexer23, i.e., an average output of about 0.256 mW in the entire channels isamplified by two-stage YDFAs 24, 25 by 60 dB (1,000,000 times) in totalis shown. In this case, at the output end of each channel, the outputlight having peak power of 20 kW, pulse width of 1 ns, pulse repetitionfrequency of 100 kHz and average output of 2 W (average output of about256 W in the entire channels) can be obtained. Further, in FIG. 3, onlythe channel 0 among all of the channels is shown and the other channelsare omitted from illustration, the other channels have same arrangementsas the arrangement of the channel 0.

The single wavelength pulse laser light having wavelength of 1.099 μm(output of the optical amplifier) is converted into ultraviolet lightpulse output light having narrow spectrum line width by the wavelengthconverting portion using the non-linear optical crystals. The wavelengthconverting portion will be described later.

In the above-mentioned first and second embodiments, although the outputwavelengths of the optical amplifiers are different, as mentioned above,the output wavelengths are determined by the oscillating wavelengths ofthe single wavelength oscillating lasers (11, 21) and are obtained by acombination of fiber optical amplifiers considering the amplifyingefficiency, i.e., gain spectral bandwidths (for example, 1530 to 1560 nmin the erbium doped fiber and 990 to 1200 nm in the ytterbium dopedfiber). Accordingly, in the illustrated embodiments of the presentinvention, regarding the single wavelength oscillating laser, fiberoptical amplifiers having gain spectral bandwidths corresponding to theoscillating wavelength may be appropriately selected and combined.Further, for example, in the first embodiment, in place of the splittersof flat plate waveguide type (14, 16), the TDM (23) used in the secondembodiment may be used, and, in the second embodiment, in place of theTDM (23), the splitters of flat plate waveguide type may be used.Further, embodiments of the wavelength converting portion will bedescribed later.

Further, in a high peak power optical fiber amplifier (19 in FIG. 1 and25 in FIG. 2) of the last stage according to the illustratedembodiments, in order to avoid increase in spectrum widths of theamplified lights due to non-linear effect in the fibers, it is desirablethat large mode diameter fiber optical amplifiers having fiber modediameters (for example, 20 to 30 μm) greater than a fiber mode diameter(for example, 5 to 6 μm) normally used for communication are used.

An example of an arrangement of optical amplifier using the large modediameter fiber optical amplifiers is shown in FIG. 4. In FIG. 4, in theoptical amplifier 42 shown by a rectangular block (shown by the dotline) and adapted to increase the mode diameters of the fibers,semiconductor lasers 43 for pumping doped fibers of large mode diameteroptical amplifiers are fiber-coupled to large mode diameter fiberscorresponding to the diameters of the doped fibers of the opticalamplifiers, so that outputs of the semiconductor lasers are inputted tothe doped fibers of the optical amplifiers by using wavelength divisionmultiplexers (WDMS) 45, 46, thereby pumping the doped fibers. Laserlight amplified in the large mode diameter fibers (optical amplifier) 42is incident on a wavelength converting portion 500, where the laserlight is converted into ultraviolet light. It is desirable that thelaser beams (signals) to be amplified and propagated through the largemode diameter fibers are mainly fundamental mode. This can be realizedby selectively using the fundamental mode mainly in a single mode fiberor a multi-mode fiber having low mode degree.

Further, particularly in FIG. 4, optical polarization coupling elements44 are disposed between the semiconductor lasers 43 and the WDMs 45 sothat the laser beams outputted from two semiconductor lasers 43 andhaving polarization directions perpendicular to each other can becombined with each other. Further, in the illustrated embodiment, whilean example that the polarization directions of the laser beams are madeto be perpendicular to each other by the optical polarization couplingelements 44 was explained, when reduction in combining efficiency forthe laser beams is permitted, the polarization directions may not beperpendicular to each other. Further, influence of return light isreduced by an isolator 404 disposed on an input side of the large modediameter fiber optical amplifier 42. In addition, a narrow band filter403 for removing ASE light generated by the fiber optical amplifier 41is provided between a fiber optical amplifier 41 having a standard modediameter and the large mode diameter fiber optical amplifier 42.Further, an pumping semiconductor laser 401 is fiber-coupled to thefiber optical amplifier 41, so that output of the semiconductor laser401 is inputted to doped fibers of the optical amplifier through a WDM402, thereby pumping the doped fibers.

According to such a method, since the semiconductor lasers 43 arecoupled to the large mode diameter fibers, the coupling efficiency tothe fibers is enhanced to thereby utilize the outputs of thesemiconductor lasers effectively. Further, by using the large modediameter fibers having the same diameter, since the loss in the WDMs 45,46 can be reduced, efficiency can be enhanced. Further, connectionbetween the front stage fiber optical amplifier 41 having the standardmode diameter and the last stage large mode diameter fiber opticalamplifier 42 is effected by using fibers having mode diameters increasedin a tapered fashion.

Further, in order to obtain high outputs in the last stage fiberamplifiers (19, 25), in place of the large mode diameter fibers (42) ofFIG. 4, a double clad fiber 410 having dual fiber clad structure may beused. FIG. 5 is a sectional view showing an example of the fiber 410. Inthis structure, ions attributing to amplification of the laser light aredoped in a core 411, so that the laser light (signal) to be amplified ispropagated in the core. An pumping semiconductor laser is coupled to afirst clad 412 surrounding the core. Since the first clad is amulti-mode and has a great area, high output pumping semiconductor laserlight can easily be transferred, and the multi-mode oscillatingsemiconductor laser can be coupled efficiently, and the exciting lightsource can be used efficiently. A second clad 413 for forming awaveguide for the first clad is formed around the first clad.

Further, although quartz fibers or silicate fibers may be used as thefiber optical amplifiers of the first and second embodiments, other thanthem, fluoride fibers (for example, ZBLAN fibers) may be used. In thefluoride fiber, erbium doping density can be increased in comparisonwith the quartz or silicate fiber, with the result that a fiber lengthrequired for amplification can be reduced. It is desirable that thefluoride fibers are applied to the last stage fiber optical amplifiers(19, 25), with the result that, by the reduction of fiber lengths,expansion of spectral bandwidth due to the non-linear effect during thepropagation of pulse lights in the fibers can be suppressed, and, forexample, a light source having the narrower spectral bandwidth requiredfor the exposure apparatus can be obtained. Particularly, the fact thatthe light source having the narrower spectral bandwidth can be used inthe exposure apparatus including a projection optical system having alarge numerical aperture is advantageous, for example, in design andmanufacture of the projection optical system.

By the way, as mentioned above, when 1.51 to 1.59 μm is used as theoutput wavelength of the fiber optical amplifier having the double cladstructure, it is preferable that not only erbium but also ytterbium aredoped in order to enhance the exciting efficiency of the semiconductorlaser. That is to say, when both erbium and ytterbium are doped, strongabsorbing wavelength of the ytterbium is extended in the vicinity of 915to 975 nm, so that a plurality of semiconductor lasers having variousdifferent oscillating wavelengths at this area are coupled by the WDMsand are coupled to the first class, with the result that, since theoutputs of the plural semiconductor lasers can be used as excitinglights, great pumping power can be achieved. Further, for example, whenpolarization coupling elements are used as the light coupling elements44 in FIG. 4, since semiconductor laser outputs light having differentpolarization directions can be coupled together, the pumping power canbe increased twice.

Further, in design of the doped fibers of the fiber optical amplifier,as is in the present invention, in an apparatus (for example, exposureapparatus) operated with predetermined given wavelength, material isselected so that gain of the fiber optical amplifier at a desiredwavelength becomes great. For example, in an ultraviolet laser apparatusfor obtaining an output wavelength (193 to 194 nm) same as that of theArF excimer laser, when the fibers of the optical amplifier are used, itis desirable that material in which the gain becomes great at thedesired wavelength (for example, 1.548 μm) is selected.

However, in the communication fiber, because of wavelength divisionmultiplexing communication, it is designed so that relatively flat gainis obtained in a wavelength area having several tens of nm in thevicinity of 1.55 μm. To this end, in a communication fiber having anonly erbium doped core as exciting medium, in order to obtain the flatgain property, aluminum and phosphorus are co-doped in a silica fiber.Thus, in such a fiber, the gain does not necessarily become great at1.548 μm. This condition is shown in FIG. 6.

FIG. 6 shows a change in fluorescent intensity property of fiber, andthe abscissa indicates wavelength and the ordinate indicates fluorescentintensity. In FIG. 6, while Al/P Silica corresponds to the communicationfiber material, when Silicate L22 shown in FIG. 6 is used, greater gaincan be obtained at 1.547 μm. Further, aluminum as doping element givesan effect for shifting a peak in the vicinity of 1.55 μm toward a longerwavelength side and phosphorus gives an effect for shifting the peaktoward a shorter wavelength side. Accordingly, in order to increase thegain in the vicinity of 1.547 μm, a small amount of phosphorus may bedoped in Silicate L22.

On the other hand, for example, when the fibers of the optical amplifier(for example, above-mentioned fibers of double clad type) having coresin which both erblum and ytterbium are doped (co-doped) are used, asshown in FIG. 7, by adding a small amount of phosphorus to the cores,higher gain can be obtained in the vicinity of 1.547 μm. Further, FIG. 7shows a change in gain with respect to wavelength when inversionpopulation is changed by changing pumping power; and the abscissaindicates wavelength and the ordinate indicates gain per unit length.

In the fiber optical amplifiers according to the first and secondembodiments, since the respective fibers are independent opticalamplifiers, the difference in gains of the optical amplifiers causesfluctuation in light outputs of the channels. Accordingly, in the laserapparatuses according to such embodiments, for example, as shown in FIG.8, it is desirable that there are provided fiber output control devices405, 406 for effecting feedback control of drive currents for thepumping semiconductor lasers (401, 43) so that light outputs from thefiber optical amplifiers becomes constant (i.e., balanced) at each ofamplifying stages by branching the outputs partially in the fiberoptical amplifiers (41, 42) of respective channels and by monitoringlight intensity. In FIG. 8, the fiber output control device 405 fordetecting the branched light from the fiber optical amplifier 41 servesto control the drive current for the semiconductor laser 401 connectedto the fiber optical amplifier 41 on the basis of a detected result, andthe fiber output control device 406 for detecting the branched lightfrom the large mode diameter fiber optical amplifier 42 serves tocontrol the drive current for the semiconductor laser 43 connected tothe large mode diameter fiber optical amplifier 42 on the basis of adetected result.

Further, as shown in FIG. 8, it is preferable that there is alsoprovided a fiber output control device 407 for effecting feedbackcontrol of drive currents for the pumping semiconductor lasers 401, 43as the entire fiber optical amplifiers (41, 42) by monitoring lightintensity at the wavelength converting portion 500 so that the lightoutput from the wavelength converting portion 500 becomes predeterminedlight output. In FIG. 8, while an example that the semiconductor lasers401, 43 are independently controlled by the fiber output control device407 was illustrated, only one of the semiconductor lasers 401, 43 may becontrolled on the basis of the light intensity detected in thewavelength converting portion 500. Further, while an example that thefiber output control device 407 branches the laser light on the way ofthe wavelength converting portion 500 and detects the intensity thereofwas explained, the laser light outputted from the output end of thewavelength converting portion 500 may be partially branched andintensity thereof may be detected. Further, in FIG. 8, the otherconstructural elements the same as those in FIG. 4 are designated by thesame reference numerals and explanation thereof will be omitted.

With the arrangement as mentioned above, since the gain of the fiberoptical amplifiers of the respective channels at the amplifying stagesare made constant, eccentric load are not generated between the fiberoptical amplifiers and even or uniform light intensity as a whole can beobtained. Further, by monitoring the light intensity in the wavelengthconverting portion 500, expected predetermined light intensity can befed back to the amplifying stages, thereby capable of obtaining desiredultraviolet light stably.

Although not shown in FIG. 8, at least one of the fiber output controldevices 405, 406, 407 is connected to the single wavelength oscillatinglaser (11 or 21) and the light modulating element (12 or 22) to effecttemperature control and current control of the single wavelengthoscillating laser and to apply drive voltage pulse to the lightmodulating element and to control timing and magnitude of the voltagepulse. Accordingly, at least one fiber output control device serves todetect intensity, center wavelength and spectral bandwidth of the pulselight (fundamental wave, or visible light wavelength-converted at leastonce in the wavelength converting portion or infrared light orultraviolet light) and to effect feedback control of the temperature ofthe single wavelength oscillating laser, thereby controlling the centerwavelength and spectral bandwidth thereof. Further, on the basis of thedetected values, the current control of the single wavelengthoscillating laser and the control of the voltage pulse applied to thelight modulating element are effected, thereby controlling intensity andoscillating interval of the pulse light and start and stop of theoscillation. Further, at least one fiber output control device serves toeffect control regarding switching between pulse oscillation andcontinuous oscillation of the single wavelength oscillating laser andcontrol of oscillation interval and spectral bandwidth in the pulseoscillation and to effect at least one of the oscillation control of thesingle wavelength oscillating laser and the control of the lightmodulating element to compensate fluctuation in output of the pulselight. Further, in FIG. 8, while the use of the large mode diameterfiber optical amplifier is under assumption, the current control of thepumping semiconductor laser (401 and the like) connected to the fiberoptical amplifier explained herein and the control of the singlewavelength oscillating laser and the light modulating element can beapplied, as it is, to the ultraviolet laser apparatuses (FIGS. 1 and 2)in which the large mode diameter fiber optical amplifiers are not used.

The output ends of the last stage fiber optical amplifiers 19, 25according to the first and second embodiments are bundled to formpredetermined bundles (114, 29). The number and configuration of thebundles are determined in accordance with the construction of thewavelength converting portion and the configuration of the requiredlight source. For example, in the illustrated embodiments, a singlebundle (114, 29, 501, 601 and the like) having a circular cross-sectionis shown. In this case, since a clad diameter of each fiber is about 125μm, a diameter (at the output end) of the bundle comprised of 128 fibersbundled together becomes about 2 mm or less. Although the bundle can beformed by using the output end of the last stage EDFA or YDFA as it is,non-doped fibers may be connected to the last stage EDFA or YDFA and thebundle may be formed at output ends of the fibers.

Further, as shown in FIG. 9, at an output end 423 of each last stagefiber 422 of the optical amplifier, it is preferable that a diameter ofa core 421 in the fiber 422 is gradually infrared toward the output endin a tapered fashion so that power density (light intensity per unitarea) of light at the output end face 423 is reduced. In this case, theconfiguration of the taper is set so that expansion of the core diameteris increased sufficiently gently toward the output end face 423 and sothat a propagation lateral mode in the fiber is maintained whilesuppressing excitation of other lateral mode to a negligible value (forexample, several mrad) when the amplified laser light is beingpropagated through the tapered portion.

By setting so, the power density of light at the output end face 423 canbe reduced, thereby greatly suppressing damage of the fiber output enddue to the laser light (which is most severe problem regarding the fiberdamage). Regarding this effect, the greater the power density of thelaser light emitted from the output end of the fiber optical amplifier(for example, the higher light intensity or the smaller the diameter ofthe core for the same power, or the smaller the number of channels fordividing the whole power) becomes, the greater such effects become.

Further, as shown in FIG. 10(a), it is preferable that a window member433 having a proper thickness which permits transmission of the laserlight is closely contacted with an output end face 434 of a last stagefiber 432, either in addition to the above-mentioned expansion of thecore diameter or independently, in dependence upon the power density.However, in FIG. 10(a), the power density is reduced only by the windowmember 433 without expanding the diameter of the core 431. As is in thefirst and second embodiments, when a plurality of fiber outputs areused, other than the method shown in FIG. 10(a) in which the windowmember is provided on the output end of each fiber, as anotherembodiment shown in FIG. 10(b), a common window member 443 may beprovided for each output group of plural fiber optical amplifiers 442.However, in FIG. 10(b), although diameters of cores 441 in the fibersare not expanded, the diameters of the cores may also be expanded.Further, the number of the fiber optical amplifiers common to the singlewindow member 443 may be changed. For example, such a number may be thetotal number of the last stage fiber optical amplifiers 19 or 25 shownin FIG. 1 or FIG. 2, i.e., 128. Further, the material for the windowmember (433 or 443) is selected appropriately (for example, opticalglass such as BK7 or quartz) in consideration of transmittance at aspectral bandwidth of the fundamental wave laser light and closecontacting ability with the fiber(s), and the close contact of thefiber(s) with the window member is achieved by means of optical contactor fusion contact.

With the arrangement as mentioned above, since the power density of thelaser light emitted from the window member becomes smaller than thepower density in the fiber core 431 or 441, the damage of the output endof the fiber due to the laser light can be suppressed. By combining theprovision of the window member with the expansion of the diameter of thecore, the damage of the output ends of the fibers which was seriousproblem in the conventional techniques can be prevented.

Further, in the aforementioned embodiments (FIGS. 1, 2, 4 and 8),examples, that the isolators 110, 111, 112, 26, 27, 404 and the like areinserted in the connecting portions in order to avoid the influence ofthe return light and the narrow band filters 113, 28, 403 are insertedin order to obtain the good EDFA amplifying property, were explained.However, the locations where the isolators or the narrow band filtersare located and the number of the isolators and/or the filters are notlimited to those in the aforementioned embodiments, but, for example,the number and locations may be appropriately determined in accordancewith the degree of accuracies required by various apparatuses (forexample, exposure apparatus) to which the present invention is applied.At least one of the isolators and the narrow band filters may not beprovided at all. Further, the narrow band filter may have hightransmittance regarding only desired single wavelength, and atransmissible spectral bandwidth of the filter may be 1 pm or less. Byusing the narrow band filter or filters in this way, noise due toamplified spontaneous emission (ASE) generated in the fiber opticalamplifier can be reduced, and reduction in amplification degree of theoutput of the fundamental wave due to ASE from the front stage fiberoptical amplifier can be suppressed.

Further, in the aforementioned embodiments, feedback control of theintensity of the pulse light in which the fiber amplifier output orintensity of the pulse light picked up by the light modulating element12 or 22 is monitored and magnitude of drive voltage pulse or offset DCvoltage applied to the light modulating element is adjusted so that theintensity of each pulse becomes equal. Further, feedback control of theoscillating timing of the laser at the output end of the fiber bundlemay be effected by detecting the laser beams generated from the pluralfiber optical amplifiers 19 or 25 and by monitoring the delay time ofthe laser beam in each channel and the oscillating interval of the laserbeams between the channels and by either controlling the timing of thedrive voltage pulse applied to the light modulating element orcontrolling the TDM 23 in FIG. 2 so that the delay time and theoscillating interval become predetermined values, respectively. Further,feedback control of the wavelength of the ultraviolet light may beeffected by detecting the wavelength of the ultraviolet light generatedfrom the wavelength converting portion 500 and by adjusting thetemperature of the single wavelength oscillating laser 11 or 21 on thebasis of the detected result.

Further, so-called feedforward control may be effected in such a mannerthat fluctuation in intensity of the pulse light picked up by the lightmodulating element 12 or 22 is detected and in which the gain of atleast one stage of the multi-stage fiber optical amplifiers (13, 18, 19or 24, 25) located at stages behind the light modulating element so asto compensate such output fluctuation. Further, feedforward control maybe effected in such a manner that output (light intensity) of thechannel having short delay time (i.e., channel from which the pulselight is emitted at early timing) is detected among the channels 0 to127 and the gain of the fiber optical amplifier (or TDM 23) iscontrolled on the basis of the detection result so that outputs of thechannels having delay time longer than that of the aforementionedchannel (i.e., channels from which pulse light are emitted at latetiming) are forward-controlled. Further, particularly in the firstembodiment shown in FIG. 1, in place of the fact that the output of eachchannel is controlled, the output of each block unit having 32 channelsmay be controlled. For example, the output of at least one channel inthe first block may be detected and the outputs of the channels in thesecond block may be controlled on the basis of the detection result.

Next, an ultraviolet laser apparatus according to a third embodiment ofthe present invention will be explained with reference to FIG. 3. Theultraviolet laser apparatus according to the third embodiment comprisesa laser generating portion including a single wavelength oscillatinglaser 31 and adapted to generate a laser beam having a singlewavelength, an optical amplifier comprised of fiber optical amplifiers33, 34 and adapted to amplify incident light, and a wavelengthconverting portion (not shown) for wavelength-converting amplifiedlight, thereby providing an ultraviolet light generating apparatuscapable of generating output wavelength the same as output wavelength(193 nm) of an ArF excimer laser or output wavelength (157 nm) of an F₂laser.

In the embodiment sown in FIG. 3, the laser generating apparatusincludes the single wavelength oscillating laser 31 for generating thelaser beam having a single wavelength, and light output of the singlewavelength oscillating laser 31 is amplified by fiber optical amplifiers33, 34. Output (amplified light) of the fiber optical amplifier 34 isincident on a wavelength converting portion (602 to 611) for exampleshown in FIG. 13. Further, an output end of the fiber optical amplifier34 corresponds to fiber bundle output ends 501 and 601 shown in FIGS. 11and 13. The wavelength converting portion includes a set of non-linearoptical crystals 602, 604, 609, 611 so that the fundamental wave emittedfrom the fiber optical amplifier (31 to 36) is converted intoultraviolet light. The wavelength converting portion according to thepresent invention will be fully described later with reference to fourthto seventh embodiments.

Now, the third embodiment will be fully explained. As the singlewavelength oscillating laser 31 (FIG. 3) for generating the laser beamhaving a single wavelength, for example, InGaAsP, DFB semiconductorlaser having an oscillating wavelength of 1.544 μm and CW output of 30mW is used. In this laser, since single longitudinal mode oscillation iseffected fundamentally, an oscillation spectrum line width can besuppressed below 0.01 pm.

The light output (continuous light) of the semiconductor laser 31 isconverted into pulse light, for example, by using a light modulatingelement 32 such as an electro-optical light modulating element or anacousto-optical light modulating element. In the illustrated embodiment,as an example, a case where the output is modulated to pulse lighthaving pulse width of 1 ns and repetition frequency of 100 kHz will beexplained. As a result of such light modulation, peak power of the pulselight outputted from the light modulating element 32 becomes 30 mW andaverage output becomes 3 μW.

Similar to the first and second embodiments, pulsated output light isamplified by a fiber optical amplifier including single stage ormulti-stage EDFA (erbium doped fiber optical amplifiers). In theillustrated embodiment, as an example, an example that amplification of58 dB (667,000 times) in total is effected by two-stage fiber opticalamplifiers 33, 34 is shown. In this case, at the output end of the fiberoptical amplifier 34, the output light having average output of 2 W canbe obtained. Although such an output end can be formed by using theoutput end of the fiber optical amplifier 34 as it is, a non-doped fibercan be coupled to the last stage fiber optical amplifier 34. Further, inthe illustrated embodiment, in order to avoid the influence of thereturn light, isolators 35, 36 are appropriately inserted in variousconnecting portions.

The single wavelength pulse laser light having wavelength of 1.544 μm(output of the optical amplifier) is converted into ultraviolet lightpulse output light having narrow spectrum line width by the wavelengthconverting portion (described later) using the non-linear opticalcrystals. Further, in the optical amplifiers (31 to 36) according to theillustrated embodiment, while the out put end is constituted by thesingle fiber optical amplifier 34, for example, a plurality of fiberoptical amplifiers (33, 34) may be prepared, together with the splitter(16) of flat plate waveguide type used in the first embodiment (FIG. 1)or the TDM (23) used in the second embodiment, and the fiber opticalamplifiers 34 may be bundled to form a fiber bundle. In this case, it ispreferable that the oscillating interval between the pulse lightsemitted from the plural optical amplifiers can be adjusted by adjustingthe timing of the drive voltage pulses applied to the light modulatingelements 32 associated with the plural optical amplifiers (for, example,the light emitting timings of the respective optical amplifiers aredeviated from each other so that the pulse lights are emittedsuccessively with equidistant interval). Further, also in thisembodiment, the above-mentioned alteration of the first and secondembodiments can be applied. For example, the single wavelengthoscillating laser 31 may be pulse-oscillated, and the oscillatinginterval (pulse period) between the pulse lights may be altered byeffecting only the current control of the single wavelength oscillatinglaser 31 or by effecting both such a current control and the control ofthe light modulating element 32.

Next, embodiments of the wavelength converting portion used in the firstto third embodiments will be described. FIGS. 11(a) to 11(d) show fourthto seventh embodiments of the wavelength converting portion according tothe present invention. In these embodiments, the fundamental wave havinga wavelength of 1.544 nm emitted from an output end 501 of the fiberbundle (which corresponds to the output end 114 in the first embodimentand the output end 29 in the second embodiment; but, which may be theoutput end of the single fiber (34) in the third embodiment) iswavelength-converted into 8th harmonic wave (harmonic wave) by using thenon-linear optical crystals, thereby generating ultraviolet light havinga wavelength the same as the wavelength (193 nm) of the ArF excimerlaser.

In FIG. 11(a), the fundamental wave having the wavelength of 1.544 nm(frequency of ω) emitted from the output end 501 of the fiber bundlepasses through non-linear optical crystals 502, 503, 504 (from left toright in FIG. 11(a)) and is outputted. When the fundamental wave ispassed through the non-linear optical crystal 502, 2nd harmonic wavehaving frequency of 2ω (wavelength of 772 nm which is ½ of thewavelength of the fundamental wave) which is twice of the frequency ω ofthe fundamental wave is generated by second harmonic wave generation.The generated 2nd harmonic wave advances to the right and enters thenext non-linear optical crystal 503. Where, the second harmonic wavegeneration is effected again, with the result that 4th harmonic wavehaving frequency of 4ω (wavelength of 386 nm which is ¼ of thewavelength of the fundamental wave) which is twice of the frequency 2ωof the incident wave, i.e., four times of the frequency ω of thefundamental wave is generated. The generated 4th harmonic wave furtheradvances to the right non-linear optical crystal 504, where, the secondharmonic wave generation is effected again, with the result that 8thharmonic wave having frequency of 8ω (wavelength of 193 nm which is ⅛ ofthe wavelength of the fundamental wave) which is twice of the frequency4ω of the incident wave, i.e., eight times of the frequency ω of thefundamental wave is generated.

Regarding the non-linear optical crystals, for example, LiB₃O₅ (LBO)crystal is used as the converting crystal 502 from the fundamental waveto 2nd harmonic wave, LiB₃O₅ (LBO) crystal is used as the convertingcrystal 503 from 2nd harmonic wave to 4th harmonic wave, and Sr₂B₂B₂O₇(SBBO) is used as the converting crystal 504 from 4th harmonic wave to8th harmonic wave. Here, in the conversion from the fundamental wave to2nd harmonic wave using the LBO crystal, a method for adjusting atemperature of the LBO crystal to achieve phase matching for wavelengthconversion (non-critical phase matching; NCPM) is used. In NCPM, sincethere is no angular deviation (Walk-off) between the fundamental waveand the second harmonic wave in the non-linear optical crystal, theconversion to 2nd harmonic wave can be effected with high efficiency,and, since the generated 2nd harmonic wave is not influenced by a beamdue to the Walk-off, it is advantageous.

FIG. 11(b) shows an embodiment in which the fundamental wave (having thewavelength of 1.544 μm) is wavelength-converted to 8th harmonic wave(having a wavelength of 193 nm) through 2nd harmonic wave (having awavelength of 772 nm), 3rd harmonic wave (having a wavelength of 515 nm)and 6th harmonic wave (having a wavelength of 257 nm) successively.

In a first stage 507 of a wavelength converting portion, LBO crystal isused for conversion from the fundamental wave to 2nd harmonic wave bysecond harmonic wave generation in NCPM. In the wavelength convertingportion (LBO crystal) 507, a part of the fundamental wave is passedwithout wavelength conversion, and the fundamental wave iswavelength-converted to generate 2nd harmonic wave, and half-wavelengthretardation and one-wavelength retardation are given to the fundamentalwave and 2nd harmonic wave, respectively by a wavelength plate (forexample, a ½ wavelength plate), and only polarization of the fundamentalwave is rotated by 90 degrees. The fundamental wave and 2nd harmonicwave are incident on a second stage wavelength converting portion 510through a lens 509.

In the second stage wavelength converting portion 510, from the 2ndharmonic wave generated in the first stage wavelength converting portion507 and the fundamental wave permeated without conversion, 3rd harmonicwave (having a wavelength of 515 μm) is obtained by sum frequencygeneration. LBO crystal is used as the wavelength converting crystal,but it is used in NCPM having a temperature different from that in thefirst stage wavelength converting portion (LBO crystal) 507. The 3rdharmonic wave obtained in the wavelength converting portion 510 and the2nd harmonic wave transmitted or passed without conversion are separatedby a dichroic mirror 511, and the 3rd harmonic wave reflected by thedichroic mirror 511 is incident on a third stage wavelength convertingportion 514 through a lens 513. The wavelength converting portion 514includes a β-BaB₂O₄ (BBO) crystal, where the 3rd harmonic wave isconverted into 6th harmonic wave (having a wavelength of 257 nm) by 2ndharmonic wave generation.

The 6th harmonic wave obtained in the wavelength converting portion 514and the 2nd harmonic wave transmitted through the dichroic mirror 511and passed through a lens 512 are combined or composed coaxially by adichroic mirror 516 and are incident on a fourth stage wavelengthconverting portion 517. The wavelength converting portion 517 includesBBO crystal, where, from the 6th harmonic wave and the 2nd harmonicwave, 8th harmonic wave (having a wavelength of 193 nm) is obtained bysum frequency generation. In the arrangement shown in FIG. 11(b), as thewavelength converting crystal in the fourth stage wavelength convertingportion 517, in place of BBO crystal, CsLiB₆O₁₀ (CLBO) crystal may beused.

Further, in the illustrated embodiment, the 3rd harmonic wave and the2nd harmonic wave obtained in the second stage converting portion 510are divided by the dichroic mirror 511 and the 6th harmonic waveobtained in the third stage wavelength converting portion 514 and the2nd harmonic wave obtained in the second stage wavelength convertingportion 510 are combined by the dichroic mirror 516 to be inputted tothe fourth stage wavelength converting portion 571. Here, the propertyof the dichroic mirror 511 may be reversed. Namely, the 3rd harmonicwave may be transmitted and the 2nd harmonic wave may be reflected andthe third stage wavelength converting portion 514 may be arranged on thesame optical axis as that of the second stage wavelength convertingportion 510. In this case, it is required that the property of thedichroic mirror 516 be also reversed. In such an arrangement in whichone of the 6th harmonic wave and 2nd harmonic wave is incident on thefourth stage wavelength converting portion 517 through the branchinglight path, collective lenses 515, 512 for inputting the 6th harmonicwave and 2nd harmonic wave to the fourth stage wavelength convertingportion 517 can be arranged in the different light paths.

Since the cross-sectional configuration of the 6th harmonic wavegenerated in the third stage wavelength converting portion 514 iselliptical due to Walk-off phenomenon, it is desirable that beam shapingof the 6th harmonic wave is effected in order to obtain the goodconversion efficiency in the fourth stage wavelength converting portion517. Thus, as is in the illustrated embodiment, by arranging thecollective lenses 515, 512 in the different light paths, for example, apair of cylindrical lenses can be used as the lens 515, thereby easilyeffecting the beam shaping of the 6th harmonic wave. Therefore, goodoverlapping with the 2nd harmonic wave in the fourth stage wavelengthconverting portion (BBO crystal) 517 can be achieved, thereby capable ofenhancing the conversion efficiency.

Further, the arrangement between the second stage wavelength convertingportion 510 and the fourth stage wavelength converting portion 517 isnot limited to that shown in FIG. 11(b), but, any arrangement can beused so long as the length of the light path of the 6th harmonic wave isthe same as that of the 2nd harmonic wave so that the 6th harmonic waveand 2nd harmonic wave are simultaneously incident on the fourth stagewavelength converting portion 517. Further, for example, the third andfourth stage wavelength converting portions 514, 517 may be arranged onthe same optical axis as that of the second stage wavelength convertingportion 510 so that only the 3rd harmonic wave is converted into the 6thharmonic wave by second harmonic wave generation in the third stagewavelength converting portion 514 and the 6th harmonic wave is incidenton the fourth stage wavelength converting portion 517 together with the2nd harmonic wave which was not wavelength-converted. In this case, thedichroic mirrors 511, 516 can be omitted.

FIG. 11(c) shows an embodiment in which the fundamental wave (having thewavelength of 1.544 μm) is wavelength-converted to 8th harmonic wave(having a wavelength of 193 nm) through 2nd harmonic wave (having awavelength of 772 nm), 4th harmonic wave (having a wavelength of 386 nm)and 6th harmonic wave (having a wavelength of 257 nm) successively.

In a first stage 518 of a wavelength converting portion, LBO crystal isused as the wavelength converting crystal for converting the fundamentalwave to 2nd harmonic wave in NCPM. The 2nd harmonic wave generated inthe first stage wavelength converting portion 518 is incident on asecond stage wavelength converting portion 520 through a collective lens519. In the second stage wavelength converting portion 520, LBO crystalis used as the wavelength converting crystal so that, from the 2ndharmonic wave generated in the first stage wavelength converting portion518, 4th harmonic wave (having a wavelength of 386 nm) is obtained bysecond harmonic wave generation. The 4th harmonic wave obtained in thewavelength converting portion 520 and the 2nd harmonic wave transmittedthrough the wavelength converting portion 520 without conversion areseparated or divided by a dichroic mirror 521, and the 4th harmonic wavereflected by the dichroic mirror reaches a dichroic mirror 525 through acollective lens 524. On the other hand, a polarization direction of the2nd harmonic wave passed through the dichroic mirror 521 is rotated by90 degrees by a half-wavelength plate 522, and the 2nd harmonic wavereaches the dichroic mirror 525 through a collective lens 523, where the2nd harmonic wave is coaxially combined with the 4th harmonic wavepassed through the branched path, and the combined wave is incident on athird stage wavelength converting portion 526.

In the third stage wavelength converting portion 526, BBO crystal isused as the wavelength converting crystal so that, from the 4th harmonicwave generated in the second stage wavelength converting portion 520 andthe 2nd harmonic wave transmitted through the wavelength convertingportion 520 without wavelength conversion, 6th harmonic wave (having awavelength of 257 nm) is obtained by sum frequency generation. The 6thharmonic wave obtained in the wavelength converting portion 526 and the2nd harmonic wave transmitted through the wavelength converting portion520 without wavelength conversion are separated by a dichroic mirror527, and a polarization direction of the 2nd harmonic wave reflectedhere is rotated by 90 degrees by a half-wavelength plate 528, and the2nd harmonic wave reaches a dichroic mirror 531 through a collectivelens 529. On the other hand, the 6th harmonic wave passed through thedichroic mirror 527 reaches the dichroic mirror 531 through a collectivelens 530, where the 6th harmonic wave is coaxially combined with the 2ndharmonic wave passed through the branched path, and the combined wavesare incident on a fourth stage wavelength converting portion 532.

In the fourth stage wavelength converting portion 532, BBO crystal isused as the wavelength converting crystal so that, from the 6th harmonicwave generated in the third stage wavelength converting portion 526 andthe 2nd harmonic wave transmitted through the wavelength convertingportion 526 without wavelength conversion, 8th harmonic wave (having awavelength of 193 nm) is obtained by sum frequency generation. With theabove arrangement, as the wavelength converting crystal in the fourthstage wavelength converting portion 532, in place of the BBO crystal,CLBO crystal may be used.

Further, in the illustrated embodiment, while an example that thedichroic mirror (521 or 527) is disposed behind the second and thirdwavelength converting portions 520, 526, respectively so that the pairof harmonic waves (2nd harmonic wave and 4th harmonic wave, or 2ndharmonic wave and 6th harmonic wave) outputted from such wavelengthconverting portion (520 or 526) are incident on the next stagewavelength converting portion (526 or 532) through the different lightpaths was explained. However, similar to the explanation in connectionwith FIG. 11(b), the third stage wavelength converting portion 526 maybe arranged on the same optical axis as those of the other wavelengthconverting portions 518, 520, 532, so that the dichroic mirrors 521,525, 527, 531 can be omitted.

By the way, in the illustrated embodiment, the 4th harmonic wave and 6thharmonic wave generated in the second and third wavelength convertingportions 520, 526 have elliptical cross-sectional configurations due toWalk-off phenomenon. Thus, it is desirable that beam shaping of the 4thharmonic wave and 6th harmonic wave (incident beams) is effected toachieve good overlapping with the 2nd harmonic wave in order to obtainthe good conversion efficiency in the third and fourth stage wavelengthconverting portions 526, 532 into which the beams are inputted. As is inthe illustrated embodiment, by arranging the collective lenses 523, 524and 529, 530 in the different light paths, for example, pairs ofcylindrical lenses can be used as the lenses 524, 530, thereby easilyeffecting the beam shaping of the 4th harmonic wave and 6th harmonicwave. Therefore, good overlapping with the 2nd harmonic wave in thethird and fourth stage wavelength converting portions 526, 532 can beachieved to thereby enhance the conversion efficiency.

Further, the arrangement between two stage wavelength convertingportions 520 and 526 is not limited to that shown in FIG. 11(c), but,any arrangement can be used so long as the length of the light path ofthe 2nd harmonic wave is the same as that of the 4th harmonic wave sothat the 2nd harmonic wave and 4th harmonic wave are simultaneouslyincident on the third stage wavelength converting portion 526. The sameis true regarding the arrangement between the third stage wavelengthconverting portion 526 and the fourth stage wavelength convertingportion 532.

FIG. 11(d) shows an embodiment in which the fundamental wave (having thewavelength of 1.544 μm) is wavelength-converted to 8th harmonic wave(having a wavelength of 193 nm) through 2nd harmonic wave (having awavelength of 772 nm), 3rd harmonic wave (having a wavelength of 515nm), 4th harmonic wave (having a wavelength of 386 nm) and 7th harmonicwave (having a wavelength of 221 nm) successively.

In a first stage 533 of a wavelength converting portion, LBO crystal isused as the wavelength converting crystal for converting the fundamentalwave to 2nd harmonic wave in NCPM. The fundamental wave transmittedthrough the wavelength converting portion 533 without wavelengthconversion and the 2nd harmonic wave generated by the wavelengthconversion are delayed by a half-wave and one-wave, respectively, bymeans of a wavelength plate 534, and a polarization direction of onlythe fundamental wave is rotated by 90 degrees. In a second stagewavelength converting portion 536, LBO crystal is used as the wavelengthconverting crystal, but it is used in NCPM having a temperaturedifferent from that in the first stage wavelength converting portion(LBO crystal) 533. In this wavelength converting portion 536, from the2nd harmonic wave generated in the first stage wavelength convertingportion 533 and the fundamental wave transmitted through the wavelengthconverting portion 533 without wavelength conversion, 3rd harmonic wave(having a wavelength of 515 nm) is obtained by sum frequency generation.

The 3rd harmonic wave obtained in the wavelength converting portion 536,and the fundamental wave and 2nd harmonic wave transmitted through thewavelength converting portion 536 without wavelength conversion aredivided or separated by a dichroic mirror 537, and the 3rd harmonic wavereflected here is incident on a fourth stage wavelength convertingportion 545 through a collective lens 540 and a dichroic mirror 543. Onthe other hand, the fundamental wave and 2nd harmonic wave passedthrough the dichroic mirror 537 are incident on a third stage wavelengthconverting portion 539 through a collective lens 538.

In the third stage wavelength converting portion 539, LBO crystal isused as the wavelength converting crystal so that the fundamental waveis transmitted through the LBO crystal without wavelength conversion andthe 2nd harmonic wave is converted into 4th harmonic wave (having awavelength of 386 nm) in the LBO crystal by second harmonic wavegeneration. The 4th harmonic wave obtained in the wavelength convertingportion 539 and the fundamental wave transmitted therethrough areseparated by the dichroic mirror 541, and the fundamental wave passedthrough the dichroic mirror passes through a collective lens 544 and isreflected by a dichroic mirror 546 and is incident on a fifth stagewavelength converting portion 548. On the other hand, the 4th harmonicwave reflected by the dichroic mirror 541 reaches a dichroic mirror 543through a collective lens 542, where it is coaxially combined with the3rd harmonic wave reflected by the dichroic mirror 537, and the combinedwaves are incident on the fourth stage wavelength converting portion545.

In the fourth stage wavelength converting portion 545, BBO crystal isused as the wavelength converting crystal so that, from the 3rd harmonicwave and 4th harmonic wave, 7th harmonic wave (having a wavelength of221 nm) is obtained by sum frequency generation. The 7th harmonic waveobtained in wavelength converting portion 545 passes through acollective lens 547 and is coaxially combined with the fundamental wave(passed through the dichroic mirror 541) by the dichroic mirror 546, andthe combined waves are incident on the fifth stage wavelength convertingportion 548.

In the fifth stage wavelength converting portion 548, LBO crystal isused as the wavelength converting crystal so that, from the fundamentalwave and 7th harmonic wave, 8th harmonic wave (having a wavelength of193 nm) is obtained by sum frequency generation. In the abovearrangement, in place of the BBO crystal 545 for the 7th harmonic waveand the LBO crystal 548 for the 8th harmonic wave, CLBO crystals can beused.

In the illustrated embodiment, since the 3rd harmonic wave and 4thharmonic wave-are incident on the fourth stage wavelength convertingportion 545 through the different light paths, the lens 540 forcollecting the 3rd harmonic wave and the lens 542 for collecting the 4thharmonic wave can be arranged in the different light paths. The 4thharmonic wave generated in the third stage wavelength converting portion539 has an elliptical cross-sectional configuration due to Walk-offphenomenon. Thus, it is desirable that beam shaping of the 4th harmonicwave is effected in order to obtain good conversion efficiency in thefourth stage wavelength converting portion 545. In the illustratedembodiment, since the collective lenses 540, 542 are disposed in thedifferent light paths, for example, a pair of cylindrical lenses can beused as the lens 542, thereby easily effecting the beam shaping of the4th harmonic wave. Thus, good overlapping with the 3rd harmonic wave inthe fourth stage wavelength converting portion (BBO crystal) 545 can beachieved, thereby enhancing the conversion efficiency.

Further, in the illustrated embodiment, the lens 544 for collecting thefundamental wave incident on the fifth stage wavelength convertingportion 548 and the lens 547 for collecting the 7th harmonic wave can bedisposed in the different light paths. The 7th harmonic wave generatedin the fourth stage wavelength converting portion 545 has an ellipticalcross-sectional configuration due to Walk-off phenomenon. Thus, it isdesirable that beam shaping of the 7th harmonic wave is effected inorder to obtain good conversion efficiency in the fifth stage wavelengthconverting portion 548. In the illustrated embodiment, since thecollective lenses 544, 547 are disposed in the different light paths,for example, a pair of cylindrical lenses can be used as the lens 547,thereby easily effecting the beam shaping of the 7th harmonic wave.Thus, good overlapping with the fundamental wave in the fifth stagewavelength converting portion (LBO crystal) 548 can be achieved, therebyenhancing the conversion efficiency.

Further, the arrangement between the second stage wavelength convertingportion 536 and the fourth stage wavelength converting portion 545 isnot limited to that shown in FIG. 11(d), but, any arrangement can beused so long as the lengths of two light paths between the wavelengthconverting portions 536 and 545 are the same so that the 3rd harmonicwave generated in the wavelength converting portion 536 and reflected bythe dichroic mirror 537 and 4th harmonic wave obtained bywavelength-converting (in the wavelength converting portion 539) the 2ndharmonic wave generated in the wavelength converting portion 536 andpassed through the dichroic mirror 537 are simultaneously incident onthe wavelength converting portion 545. This is also true regarding thearrangement between the third stage wavelength converting portion 539and the fifth stage wavelength converting portion 548.

FIGS. 12(a) to 12(d) show wavelength conversion efficiency and averageoutput of the obtained 8th harmonic wave (having wavelength of 193 nm)for each channel in each stage obtained from test results regarding thewavelength converting portions shown in FIGS. 11(a) to 11(d). Asexplained in the above-mentioned embodiment, the output of thefundamental wave has peak power of 20 kW, pulse width of 1 ns, pulserepeating frequency of 100 kHz and average output of 2 W. As a result,it was found that the average of the 8th harmonic wave (havingwavelength of 193 nm) for each channel becomes 229 mW (in the wavelengthconverting portion shown in FIG. 11(a)), 38.3 mW (in the wavelengthconverting portion shown in FIG. 11(b)), 40.3 mW (in the wavelengthconverting portion shown in FIG. 11(c)) and 45.9 mW (in the wavelengthconverting portion shown in FIG. 11(d)). Accordingly, the average outputfrom the bundle obtained by bundling all 128 channels becomes 29 W (inFIG. 11(a)), 4.9 W (in FIG. 11(b)), 5.2 W (in FIG. 11(c)). and 5.9 W (inFIG. 11(b)), and, thus, in all of the wavelength converting portions,the ultraviolet light (having wavelength of 193 nm) having adequateoutput for the light source of the exposure apparatus can be provided.

Among these embodiments, the arrangement shown in FIG. 11(a) is mostsimple and provides highest conversion efficiency. Thus, the ultravioletlight (having wavelength of 193 nm) having adequate output for the lightsource of the exposure apparatus can be provided even when the number ofchannels of the fiber optical amplifier is reduced in comparison withthe channel number (128 channels) in the first and second embodiments(for example, reduced to ½ to ⅓ and the bundle is formed) or even whenoutput of the fundamental wave lower than the fundamental wave output inthe aforementioned embodiment is used.

In the arrangement shown in FIG. 11(d), although the number (five) ofthe stages of the wavelength converting portion is greatest among theembodiments, the conversion efficiency to the wavelength of 193 nm issubstantially the same as those in the embodiments shown in FIGS. 11(b)and 11(c) and the substantially the same ultraviolet light can beobtained. Further, in the arrangements shown in FIGS. 11(b) and 11(c),since the BBO crystal is used for generating the 8-time wave, the 8thharmonic wave is absorbed by the BBO crystal, with the result that theBBO crystal may be damaged. To the contrary, in the arrangement shown inFIG. 11(d), LBO crystal can be used for generating 8th harmonic wave.The LBO crystal can easily available from a market as good qualitycrystal in which an absorbing coefficient for ultraviolet light havingwavelength of 193 nm in very small and which does not arise any lightdamage problem, and-the LBO crystal is advantageous from the view pointof its endurance. Further, in the 8th harmonic wave (for example,wavelength of 193 nm) generating portion, although LBO crystals are usedunder angular phase matching condition, since the phase matching angleis great, the effective non-linear optical constant (d_(eff)) becomessmall. To this end, it is preferable that a temperature controllingmechanism is provided in association with the LBO crystal and the LBOcrystal is used under a high temperature condition. As a result, thephase matching angle can be reduced, namely, the constant (d_(eff)) canbe increased, thereby improving the 8th harmonic wave generatingefficiency.

Further, in the above explanation, while preferred embodiments of thearrangement of the wavelength converting portion in which the 8thharmonic wave is generated from the fundamental wave was explained, thewavelength converting portion according to the present invention is notlimited to such embodiments, so long as a wave having a wavelengthgreater than the wavelength (1.544 μm) of the fundamental wave by eighttimes is generated, the same effect can be achieved. For example, bywavelength-converting the fundamental wave (having wavelength of 1.544μm) to 8th harmonic wave (having wavelength of 193 nm) through 2ndharmonic wave (having wavelength of 772 nm), 3rd harmonic wave (havingwavelength of 515 nm), 4th harmonic wave (having wavelength of 386 nm),6th harmonic wave (having wavelength of 257 nm) and 7th harmonic wave(having wavelength of 221 nm), successively, similar effect can beachieved.

In this case, as the non-linear optical crystals used in wavelengthconversion, LBO crystal can be used as the converting crystal forconverting the fundamental wave into the 2nd harmonic wave, LBO crystalcan be used as the converting crystal for converting the 2nd harmonicwave into the 4th harmonic wave, BBO crystal can be used for generatingthe 6th harmonic wave by sum frequency generation based on the 2ndharmonic wave and 4th harmonic wave, BBO crystal can be used forgenerating the 7th harmonic wave by sum frequency generation based onthe fundamental wave and the 6th harmonic wave, and LBO crystal can beused for generating the 8th harmonic wave by sum frequency generationbased on the fundamental wave and the 7th harmonic wave. Also in thiscase, since the LBO crystal can be used for generating the 8th harmonicwave, any problem regarding the damage of the crystal does not arise,and, thus, usage of the LBO crystal is advantageous.

By arranging the wavelength converting portion as the fourth embodiment,the fundamental wave having the wavelength of 1.544 μm and generated bythe fundamental wave generating portion can be wavelength-converted intothe ultraviolet light having the wavelength of 193 nm.

Next, a further arrangement of a wavelength converting portion accordingto the present invention is shown in FIG. 13 as a fifth embodiment. Inthis embodiment, the fundamental wave having a wavelength of 1.57 μm andemitted from an output end 601 (corresponding to the output end 114 inthe first embodiment and output end 29 in the second embodiment) of afiber bundle is subjected to harmonic wave generation from 10th harmonicwave by using non-linear optical crystals, thereby generatingultraviolet light having a wavelength of 157 nm the same as that of theF₂ laser. Further, as the fundamental wave generating portion accordingto this embodiment, the fundamental wave generating portion in eitherone of the first to third embodiments or combination thereof can beused.

In the arrangement of the wave length converting portion shown in FIG.13, the fundamental wave (having wavelength of 1.57 μm) iswavelength-converted into 10th harmonic wave (having wavelength of 157nm) through 2nd harmonic wave (having wavelength of 785 nm), 4thharmonic wave (having wavelength of 392.5 nm) and 8th harmonic wave(having wavelength of 196.25 nm) successively. In the illustratedembodiment, in wavelength converting stages from 2nd harmonic wavegeneration to 8th harmonic wave generation, wavelength incident on therespective wavelength converting stages are subjected to second harmonicwave generation.

Further, in the illustrated embodiment, as the non-linear opticalcrystals, LBO crystal is used for generating the 2nd harmonic wave fromthe fundamental wave based on second harmonic wave generation in awavelength converting portion 602, and LBO crystal is used forgenerating the 4th harmonic wave from the 2nd harmonic wave based onsecond harmonic wave generation in a wavelength converting portion 604.Further, Sr₂Be₂B₂O₇ (SBBO) crystal is used for generating the 8thharmonic wave from the 4th harmonic wave based on second harmonic wavegeneration in a wavelength converting portion 609, and SBBO crystal isused for generating the 10th harmonic wave (having wavelength of 157 nm)based on sum frequency generation of the 2nd harmonic wave and the 8thharmonic wave in a wavelength converting portion 611.

Further, the 2nd harmonic wave generated from the wavelength convertingportion 602 is incident on the wavelength converting portion 604 througha collective lens 603, which wavelength converting portion 604 generatesthe 4th harmonic wave, and 2nd harmonic wave which is notwavelength-converted. Then, the 2nd harmonic wave passed through adichroic mirror 605 passes through a collective lens 606 and isreflected by a dichroic mirror 607 to be incident on the wavelengthconverting portion 611. On the other hand, the 4th harmonic wavereflected by the dichroic mirror 605 passes through a collective lens608 and is incident on the wavelength converting portion 609, and the8th harmonic wave generated here passes through a collective lens 610and the dichroic mirror 607 and is incident on the wavelength convertingportion 611. Further, in the wavelength converting portion 611, from the2nd harmonic wave and the 8th harmonic wave which are coaxiallycombined, the 10th harmonic wave (having wavelength of 157 nm) isgenerated on the basis of the sum frequency generation.

By the way, in the illustrated embodiment, an example that, by branchingthe 2nd harmonic wave and the 4th harmonic wave generated by the secondstage wavelength converting portion 604 by the dichroic mirror 605, the2nd harmonic wave passed therethrough and the 8th harmonic wave obtainedby wavelength-converting the 4th harmonic wave in the wavelengthconverting portion 609 are incident on the fourth stage wavelengthconverting portion 611 through different light paths was explained.However, four wavelength converting portions 602, 604, 609, 611 may bearranged on the same optical axis without using the dichroic mirrors605, 607.

However, in the illustrated embodiment, the 4th harmonic wave generatedin the second stage wavelength converting portion 604 has an ellipticalcross-sectional configuration due to Walk-off phenomenon. Thus, it isdesirable that beam shaping of the 4th harmonic wave (incident beam) iseffected to improve overlapping with the 2nd harmonic wave in order toobtain good conversion efficiency in the fourth stage wavelengthconverting portion 611 on which the beam is incident. In the illustratedembodiment, since the collective lenses 606, 608 can be arranged on thedifferent light paths, for example, a cylindrical lens can be used asthe lens 608, thereby easily effecting the beam shaping of the 4thharmonic wave. Thus, the overlapping with the 2nd harmonic wave in thefourth stage wavelength converting portion 611 can be improved and theconversion efficiency can be enhanced.

By designing the wavelength converting portion as shown in the fifthembodiment, the fundamental wave (having wavelength of 1.57 μm)generated at the fundamental wave generating portion can be convertedinto the ultraviolet light having wavelength of 157 nm.

A still further arrangement of a wavelength converting portion accordingto the present invention is shown in FIG. 14 as a sixth embodiment. Inthis embodiment, for example, the fundamental wave generating portion asshown in the second embodiment is designed, and the fundamental wavehaving a wavelength of 1.099 μm and emitted from an output end 701(corresponding to the output end 114 in the first embodiment and outputend 29 in the second embodiment) of a fiber bundle is subjected toharmonic wave generation from 7th harmonic wave by using non-linearoptical crystals, thereby generating ultraviolet light having awavelength of 157 nm the same as that of the F₂ laser. Further, as thefundamental wave generating portion according to this embodiment, thefundamental wave generating portion in either one of the first to thirdembodiments or combination thereof can be used.

In the arrangement of the wave length converting portion shown in FIG.14, the fundamental wave (having wavelength of 1.099 μm) iswavelength-converted into 7th harmonic wave (having wavelength of 157nm) through 2nd harmonic wave (having wavelength of 549.5 nm), 3rdharmonic wave (having wavelength of 366.3 nm) and 4th harmonic wave(having wavelength of 274.8 nm) successively. In theillustrated-embodiment, in each of wavelength converting stages, secondharmonic wave generation or sum frequency generation of the incidentlight is effected.

In this embodiment, LBO crystal is used for generating the 2nd harmonicwave from the fundamental wave on the basis of second harmonic wavegeneration in a wavelength converting portion 702, and LBO crystal isused for generating the 3rd harmonic wave on the basis of sum frequencygeneration of the fundamental wave and the 2nd harmonic wave in awavelength converting portion 705. Further, BBO crystal is used forgenerating the 4th harmonic wave from the 2nd harmonic wave on the basisof second harmonic wave generation in a wavelength converting portion710, SBBO crystal is used for generating the 7th harmonic wave on thebasis of sum frequency generation of the 3rd harmonic wave and the 4thharmonic wave in a wavelength converting portion 712.

Further, the fundamental wave and the 2nd harmonic wave generated fromthe wavelength converting portion (LBO crystal) 702 are incident on ahalf-wavelength plate 703, where only a polarization direction of thefundamental wave is rotated by 90 degrees, and the waves are incident onthe wavelength converting portion (LBO crystal) 705 through a collectivelens 704. In the wavelength converting portion 705, the 3rd harmonicwave is obtained from the fundamental wave and the 2nd harmonic wave onthe basis of sum frequency generation and the 2nd harmonic wave ispassed without wavelength conversion. The 2nd harmonic wave and the 3rdharmonic wave emitted from the wavelength converting portion 705 arebranched by a dichroic mirror 706, and the 3rd harmonic wave passed thedichroic mirror passes through a collective lens 707 and is reflected bya dichroic mirror 708 to be incident on the wavelength convertingportion 712. On the other hand, the 2nd harmonic wave reflected by thedichroic mirror 706 passes through a collective lens 709 and is incidenton the wavelength converting portion 710, where the 4th harmonic wave isgenerated from the 2nd harmonic wave on the basis of second harmonicwave generation. The 4th harmonic wave passes through a collective lens711 and the dichroic mirror 708 and is incident on the wavelengthconverting portion 712, where the 7th harmonic wave is generated fromthe 3rd harmonic wave and the 4th harmonic wave on the basis of sumfrequency generation.

By the way, in the illustrated embodiment, while an example that, bybranching the 2nd harmonic wave and the 3rd harmonic wave emitted fromthe second stage wavelength converting portion 705, the 3rd harmonicwave passed through this converting portion and the 4th harmonic waveobtained by wavelength-converting the 2nd harmonic wave in thewavelength converting portion 710 are incident on the fourth stagewavelength converting portion 712 through the different light paths wasexplained, four wavelength converting portions 702, 705, 710, 712 may bearranged on the same optical axis without using the dichroic mirrors706, 708.

However, in the illustrated embodiment, the 4th harmonic wave generatedin the third stage wavelength converting portion 710 has an ellipticalcross-sectional configuration due to Walk-off phenomenon. Thus, it isdesirable that beam shaping of the 4th harmonic wave (incident beam) iseffected to improve overlapping with the 3rd harmonic wave in order toobtain good conversion efficiency in the fourth stage wavelengthconverting portion 712 on which the beam is incident. In the illustratedembodiment, since the collective lenses 707, 711 can be arranged on thedifferent light paths, for example, a cylindrical lens can be used asthe lens 711, thereby easily effecting the beam shaping of the 4thharmonic wave. Thus, the overlapping with the 3rd harmonic wave in thefourth stage wavelength converting portion 712 can be improved and theconversion efficiency can be enhanced.

By designing the wavelength converting portion as shown in the sixthembodiment, the fundamental wave (having wavelength of 1.099 μm)generated at the fundamental wave generating portion can be convertedinto the ultraviolet light having wavelength of 157 nm.

Next, another arrangement of an optical amplifier and a wavelengthconverting portion according to the present invention is shown in FIG.15 as a seventh embodiment. In FIG. 15, a wavelength converting portionis constituted by a plurality of parallel light paths (squarearrangement having 4 light paths in this example), and output ends ofmany fiber optical amplifiers 19 or 25 are divided into four bundles.(output groups) accordingly, and light collecting optical elements andwavelength converting portions are provided corresponding to such fourfiber bundle output ends. In this embodiment, since it is assumed thatthe optical amplifiers shown in FIG. 1 or FIG. 2 are used, 32 fiberoptical amplifiers 19 or 25 are bundled as a single fiber bundle.Further, although the bundle can be formed by using the output end ofthe last stage EDFA or YDFA as it is, nondoped fibers may be connectedto the last stage EDFA or YDFA and the bundle may be formed at outputends of the fibers.

Further, when the output ends of the fiber optical amplifiers 19 or 25are divided to form plural fiber bundles, it is preferable that, amongthe plural (128 in the illustrated embodiment) fiber optical amplifiers19 or 25, output ends (fiber optical amplifiers) adjacent to each otherregarding the laser beam emitting sequence or order are bundled asdifferent bundles. For example, when 128 fiber optical amplifiers (19 or25) are numbered as 0 to 127 according to the light beam emittingsequence, the fiber optical amplifiers having Nos. 0, 4, 8, . . . , 124are bundled together as a first bundle, the fiber optical amplifiershaving Nos. 1, 5, 9, . . . , 125 are bundled together as a secondbundle, the fiber optical amplifiers having Nos. 2, 6, 10, . . . , 126are bundled together as a third bundle, and the fiber optical amplifiershaving Nos. 3, 7, 11, . . . , 127 are bundled together as a fourthbundle. As a result-time intervals of the pulse lights incident onwavelength converting portions (non-linear optical crystals) provided incorrespondence to the fiber bundles can be divided uniformly or equally.

As shown in FIG. 15, in the illustrated embodiment, the fundamental waveemitted from an output end 841 of the optical amplifier (FIG. 1 or FIG.2) comprised of each of four fiber bundles is wavelength-converted bythree stage wavelength converting portions 842, 843, 844. Further, inthe illustrated embodiment, although any wavelength converting portions(FIGS. 11, 13 and 14) explained in connection with the fourth to sixthembodiments can be used, here, the wavelength converting portion shownin FIG. 11(a) is used. Namely, the fundamental wave (having wavelengthof 1.544 μm) is wavelength-converted into ultraviolet light having awavelength of 193 nm by three stage non-linear optical crystals (502 to504). Accordingly, the fundamental wave (having wavelength of 1.544 μm;frequency of ω) is converted into 8th harmonic wave (having wavelengthof 193 nm) through 2nd harmonic wave and 4th harmonic wave successivelywhile passing through the non-linear optical crystals 842, 843, 844 fromthe left to the right and then is outputted.

In FIG. 15, the fundamental wave (having wavelength of 1.544 μm) emittedfrom the output end 841 of the optical amplifier comprised of four fiberbundles is incident on the wavelength converting portion (non-linearoptical crystal) 842 through collective lens 845 provided incorrespondence to four fiber bundles, and, in this wavelength convertingportion, two-time wave (having wavelength of 772 nm; frequency of 2ω)having frequency of twice of the frequency (ω) of the fundamental waveis generated by second harmonic wave generation. The 2nd harmonic wavegenerated in the wavelength converting portion 842 advances to the rightand is incident on the next wavelength converting portion (nonlinearoptical crystal) 843 through a collective lens 846. In this wavelengthconverting portion, the second harmonic wave generation is effectedagain, with the result that 4th harmonic wave having frequency of 4ω(wavelength of 386 nm) greater than the frequency 2ω of the incidentwave (2nd harmonic wave) by two times (i.e., greater than the frequencyof the fundamental wave by four times) is generated. The 4th harmonicwave generated in the wavelength converting portion 843 is incident onthe further right wavelength converting portion (non-linear opticalcrystal) 844 through a collective lens 847. In this wavelengthconverting portion, the second harmonic wave generation is effected,with the result that 8th harmonic wave having frequency of 8ω(wavelength of 193 nm) greater than the frequency 4ω of the incidentwave (4th harmonic wave) by two times (i.e., greater than the frequencyof the fundamental wave by eight times) is generated.

In this embodiment, as the non-linear crystals used for the wavelengthconversion, for example, LBO crystal is used as the wavelengthconverting crystal for converting the fundamental wave into the 2ndharmonic wave in the wavelength converting portion 842, BBO crystal isused as the wavelength converting crystal for converting the 2ndharmonic wave into the 4th harmonic wave in the wavelength convertingportion 843, and SBBO crystal is used as the wavelength convertingcrystal for converting the 4th harmonic wave into the 8th harmonic wavein the wavelength converting portion 844.

Further, in the illustrated embodiment, while an example that thefundamental wave (having wavelength of 1.544 μm) is wavelength-convertedinto the 8th harmonic wave (having wavelength of 193 nm) through the 2ndharmonic wave (having wavelength of 772 nm) and the 4th harmonic wave(having wavelength of 386 nm) successively was explained, thiscorresponds to an arrangement in which a plurality of wavelengthconverting portions (FIG. 11(a)) in the aforementioned fourth embodimentare arranged in parallel. Accordingly, by arranging a plurality of otherwavelength converting portions shown in FIG. 11(b), 11(c) or 11(d) inparallel similar to this embodiment, the arrangement similar to thisembodiment can be obtained. Similarly, a plurality of wavelengthconverting portions shown in FIG. 13 or 14 may be arranged in parallelto obtain the similar arrangement.

Next, with reference to FIG. 16, an alteration of the connectingportions between the optical amplifiers and the wavelength convertingportions in the illustrated embodiment will be explained. In thisalteration (embodiment), the wavelength converting portions shown inFIG. 15 are arranged in parallel as five light paths, and the outputends of the fiber optical amplifiers are divided into five to form fivefiber bundles (output groups). In this division, the output ends of thefiber optical amplifiers are not divided uniformly or equally, but, anoutput end 850 of part(s) (one fiber bundle in FIG. 15) of five fiberbundles (output groups) is constituted by a single fiber opticalamplifier or several fiber optical amplifiers, and the other (four inFIG. 15) fiber bundle output ends 851 are obtained by bundling theplural fiber optical amplifiers divided uniformly so that the number ofthe fiber optical amplifiers in the fiber bundles becomes the same.Output lights emitted from the output ends are converted intoultraviolet lights having predetermined wavelengths by wavelengthconverting portions 852 to 857 provided at the respective output groups(fiber bundles) and are supplied to the exposure apparatus, for example.Further, three stage wavelength converting portions 852 to 854 areconstituted by wavelength converting portions, the number of which isthe same as that of the plural (five) fiber bundles, and the lightcollecting optical elements 855 to 857 are constituted by collectivelenses, the number of which is the same as that of respective fiberbundles.

When an ultraviolet-laser apparatus according to this example is appliedto an exposure apparatus (FIG. 19 or 20), the fundamental waves emittedfrom the output ends 851 of four fiber bundles are converted into theultraviolet lights in the wavelength converting portions (852 to 857),respectively, and the ultraviolet lights are illuminated on a reticle asexposure illumination light through an illumination optical system. Thatis to say, the four fiber bundles are used as an exposure light source.On the other hand, the output light emitted from the output end 850 ofthe fiber bundle constituted by the single fiber optical amplifier orseveral fiber optical amplifiers and converted into the ultravioletlight is directed to an alignment system or a monitoring system. That isto say, one fiber bundle (850) is used as an alignment light source.Further, the ultraviolet light emitted from the fiber bundle output end850 and wavelength-converted is transmitted to the alignment systemthrough a non-doped fiber connected to the third stage wavelengthconverting portion 854, for example.

By the way, in FIG. 16, while an example that the fundamental wavesgenerated from output ends 851 of four fiber bundles arewavelength-converted into the ultraviolet lights which are in turndirected to the illumination. optical system was explained, the numberof fiber bundles may be one or plural. Further, in the example in FIG.16, the number of fiber bundle used in the alignment or the monitoringis one. However, such a number may be plural, and lights emitted fromthe plural fiber bundles may be directed to different optical systems.

In this example, the exposure light source is the same as the lightsource used in the alignment or the monitoring, and the exposureillumination light and the alignment illumination light are obtained bybranching, amplifying and wavelength-converting the output light fromthe common single-wavelength oscillating laser, and thus, ultravioletlights having the same wavelength can be used. Thus, the alignment andvarious monitoring operations can be effected through optical systems ofthe exposure apparatus such as illumination optical system andprojection optical system. Accordingly, the alignment optical system caneasily be designed to greatly facilitate construction thereof or is notrequired to be provided additionally, thereby easily constructing theexposure apparatus. Further, since there is a case where illumination ofthe exposure illumination light and illumination of the alignmentillumination light may not be effected simultaneously, it is preferablethat, for example, by providing shutters in the illumination light pathsor by selecting the channel for branching the pulse light by means ofthe TDM 23, the timings of illuminations are controlled independently.

Further, in order to measure a focus position, projectiondemagnification, aberration and telecentricity of the projection opticalsystem, the ultraviolet light for the alignment or the monitoring can beused, thereby enhancing measuring accuracy. Further, when alignmentbetween a focusing plane of the projection optical system and aphotosensitive substrate (wafer) is effected, by using light having thesame wavelength as the exposure wavelength and by effecting thealignment through the projection optical system, the aligning accuracycan be achieved simultaneously.

By the way, according to the above-mentioned arrangement of theillustrated embodiments (FIGS. 15 and 16), by dividing the outputs ofthe fiber optical amplifiers into plural groups to divide the lights fedto the non-linear crystals, incident powers fed to the non-linearcrystals can be reduced effectively. Accordingly, problems regardingoutput reduction and light damage due to light absorption and heateffect in the non-linear crystal can be solved. Further, the number ofdivision (the number of fiber bundles) of the output ends of the fiberoptical amplifiers is not limited to four or five but may be two ormore.

Next, the connecting portions between the optical amplifiers and thewavelength converting portions will be explained as an eighthembodiment. Here, the output end of the optical amplifiers is formed bybundling the output ends of the fiber optical amplifiers as a bundle asis in the first and second embodiments. In this case, since a claddiameter of the fiber optical amplifier is about 125 μm, a diameter ofthe output end of the bundle obtained by bundling 128 optical amplifierscan be smaller than about 2 mm.

The number and configuration of the bundle can be determined inconsideration of arrangements of the wavelength converting portions andthe shape of the light source required, and, for example, in the firstand second embodiments, a bundle having a single circular cross-sectionis shown (114, 29, 501, 601, 701 and the like). In this case, when theoutput end of the fiber optical amplifier is formed to be a flat planefor example as shown in FIG. 9 or 10, by providing a collective lens(for example, collective lens 845 in FIG. 15 and the like) between theoutput end of the fiber bundle and the first stage wavelength convertingportion (non-linear crystal) to collect the light generated from thefiber bundle onto the non-linear crystal, the output light from thefiber optical amplifier can be entered effectively.

Further, another example of the connecting portion according to thepresent invention is shown in FIG. 17. In FIG. 17, fundamental waves areemitted from a fiber bundle output end 901 obtained by bundling outletends of plural fiber optical amplifiers. Lenses 902 are provided inassociation with the respective fiber optical amplifiers so that thefundamental waves are collected in a first stage wavelength convertingportion (non-linear crystal) 903 (for example, 502, 507, 518, 533 in thefourth embodiment; FIG. 11) by these lenses 902. In this example, theentire diameter of the fiber bundle is selected to be 2 mm and a modediameter of each of the fiber optical amplifiers constituting the fiberbundle is selected to be 20 μm, and the fundamental waves are collectedto the first stage wavelength converting portion 903 by the respectivelenses 902. Further, a pair of lenses 904, 905 are disposed between thefirst stage wavelength converting portion 903 and a second stagewavelength converting portion 906 so that the lights emitted from thewavelength converting portion 903 are incident on the wavelengthconverting portion 906 under the same condition as that where suchlights are incident on the wavelength converting portion 903.

In such an embodiment, magnification of each lens 902 is selected (forexample, to about ten times in the illustrated embodiment) so that eachbeam diameter in the non-linear crystal becomes magnitude (for example,200 μm in the illustrated embodiment) desired to obtain the optimumharmonic wave conversion efficiency. Since the fiber outputs arecollected by independent lenses 902, magnitude (cross-sectional area) ofentire light fluxes (collected from all of the fibers in the fiberbundle) in the non-linear crystal becomes a value substantiallycorresponding to the diameter of the fiber bundle itself regardless ofthe magnification of the collective lens. Accordingly, since requiredmagnitude (cross-section) of the wavelength converting crystal becomes avalue substantially corresponding to the diameter of the fiber bundle, asmall, wavelength converting crystal having dimension of several squaremillimeters can be used, and this is therefore economical. Further, inplace of the lenses 902, the output end face of each fiber may directlybe formed as a spherical or non-spherical lens having a light collectingfunction.

Next, other embodiments of the fiber output end in the connectingportion between the optical amplifier and the wavelength convertingportion are shown in FIGS. 18(a) to 18(c). The embodiments shown inFIGS. 18(a) and 18(c) are examples that a light collecting elementsimilar to the collective lens 902 shown in FIG. 17 is formed on theoutput end of each fiber 452, and, such fibers are gathered as a bundlefor each output group, respectively. In these embodiments, although thelight collecting element 453 is formed on the output end of each fiber452, this is obtained by machining the window member 433 as a lens,which member 433 is provided on the-fiber output end already explainedin connection with FIG. 10(a) to have a light collecting function. Byconstructing in this way, the light collecting function similar to thatin FIG. 17 can be achieved and damage on the fiber output end can besuppressed.

Further, FIG. 18(b) shows an embodiment in which a light collectingelement 463 is provided with respect to each output group obtained bybundling a plurality of fibers 462. In this embodiment, for example, alight collecting element similar to the collective lens 845 shown inFIG. 15 is formed on the output end of the fiber bundle, and, this isobtained by machining the window member 443 already explained inconnection with FIG. 10(b) as a spherical or non-spherical lens to havea light collecting function.

Further, in place of the fact that the fiber end or the output surfaceof the window member is machined as the spherical or non-spherical lens,the fiber end (or glass composition of an end portion of a glass windowwhen such a glass window is used as the window member) may be partiallychanged or altered by ion exchange by using an ion exchanging methodsuch as thermal ion exchanging method or electrolytic ion exchangingmethod to have refractive index distribution equal to a lens, therebyproviding the light collecting function. Further, in FIGS. 18(a) to18(c), although diameters of cores 451, 461 in the fibers are notenlarged, enlargement of the cores may be used in combination.

Similar to the first stage, although the light collecting onto thesecond and further wavelength converting portions (non-linear crystals)can be effected by the lenses for each fiber or each bundle, in theillustrated embodiment, an example that all outputs from the fiberbundles are collected by a set of common lenses or a single common lensis described. By using the common lens(es) in this way, the number oflenses used can be reduced and the alignment between the lenses isfacilitated. Thus, this is economical.

Further, since the output ends of the wavelength converting portions(non-linear crystals) are located within Rayleigh length of the beamscollected in the wavelength converting crystals, beams emitted from thewavelength converting crystals become substantially in parallel at theoutput ends of the wavelength converting crystals. In the illustratedembodiment (FIG. 17), the emitted beams are collected into the secondstage wavelength converting crystal 906 by a pair of lenses 904, 905.Here, a focal length of the lens pair can be selected to realize themagnification such that beam diameters desirable to obtain optimumconversion efficiency in the second stage wavelength converting portion906 are obtained. Further, in FIGS. 11, 13 and 14, while an example thatthe light collecting element (for example, 505, 506 shown in FIG. 11(a))for collecting the fundamental wave or the harmonic wave thereof intothe wavelength converting crystal is constituted by the single lens wasexplained, as is in the illustrated embodiment, a set of lenses can beused.

In this way, by constructing the fundamental wave generating portion(laser light generating portion and optical amplifier) on the basis ofthe construction.shown in the first to third embodiments and byconstructing the wavelength converting portion on the basis of theconstruction shown in the fourth to seventh embodiments and byconstructing the connecting portion between the optical amplifier andthe wavelength converting portion on the basis of the construction shownin the eight embodiment, the ultraviolet light outputs light havingoutput wavelengths of 157 nm and 193 nm can be obtained. Thesewavelengths are the same as the oscillating wavelengths of the F₂ laserand ArF excimer laser.

Further, for example, when the fundamental wave generating portionaccording to the first embodiment is used, since the ultraviolet outputlights obtained in this way are pulse lights emitted with interval ofabout 3 ns, they are not overlapped with each other in a time-lapserelation, and the respective output lights do not interfere with eachother while each output light has a single wavelength with extremelynarrow band. Further, for example, when the fundamental wave generatingportion according to the second embodiment is used, since theultraviolet output lights obtained are pulse lights emitted withinterval of about 78 ns, they are not overlapped with each other in atime-lapse relation, and the respective output lights do not interferewith each other while each output light has a single wavelength withextremely narrow band.

Further, for example, in a solid-state ultraviolet laser as disclosed inJapanese Patent Laid-open No. 8-334803 (1996), although wavelengthconverting portions are required for respective fundamental wave lasers(for respective laser elements), according to the illustratedembodiment, since the entire diameter of the fiber bundles including allchannels is 2 mm or less, the wavelengths of all channels can beconverted by only one set of wavelength converting portions.Furthermore, since the output end is constituted by the flexible fibers,the wavelength converting portions can be located apart from otherconstructural parts such as the single-wavelength oscillating laser,splitter and time division multiplexer, thereby providing high degree offreedom of arrangement. Accordingly, the present invention can providean ultraviolet laser apparatus which is cheap and compact and of lowspatial coherence although it handles single wavelength.

Next, a ninth embodiment of an ultraviolet laser apparatus according tothe present invention will be explained. The ultraviolet laser apparatusaccording to this embodiment is characterized in that the ultravioletlaser apparatus such as described in the first to eighth embodiments isused as a light source of the exposure apparatus.

Now, an embodiment of the exposure apparatus using the ultraviolet laserapparatus according to the present invention will be explained withreference to FIG. 19. In principle, the exposure apparatus used in aphoto-lithography process is the same as photoengraving, in which acircuit pattern precisely described on a photo-mask (reticle) isoptically transferred on a semiconductor wafer on which photo-resist iscoated in a reduction projection manner. The ultraviolet laser apparatus1261 according to the present invention is integrally provided with theentire exposure apparatus including an illumination optical system 1262and a projection optical system 1265. In this case, the ultravioletapparatus 1261 may be secured to a table supporting the illuminationoptical system 1262 or the ultraviolet apparatus 1261 may be secured tothe table solely. However, it is preferable that a power supplyconnected to the ultraviolet apparatus 1261 be located separately.

Further, the ultraviolet apparatus 1261 may be divided into a first partincluding the laser light generating portion and the optical amplifiersand a second part including the wavelength converting portions, and thesecond part may be secured to the table together with the illuminationoptical system 1262 and the first part may be secured to a tabledifferent from the aforementioned table. Further, the entire ultravioletapparatus 1261 may be housed in a chamber containing the body of theexposure apparatus, or a part of the ultraviolet apparatus 1261 (forexample, wavelength converting portions) may be housed and the remainingparts may be arranged out of the chamber. Furthermore, the controlsystem for the ultraviolet apparatus 1261 may be housed in a controlrack different from the chamber, or the display and switches may bepositioned together with the chamber outside and the remaining parts maybe housed in the chamber.

The ultraviolet light having low spatial coherence and having narrowband according to the present invention is projected with an enlargingmagnification by the illumination optical system 1262 so thatilluminance distribution on the required projection plane is madeuniform, and is illuminated onto a quartz mask (quartz reticle) 1263 onwhich a circuit pattern of an IC circuit is precisely described. Thecircuit pattern on the reticle is subjected to reduction withpredetermined reduction magnification (or demagnification) by theprojection optical system 1265 and is projected onto the semiconductorwafer (for example, Silicone wafer) 1266 on which photo-resist iscoated, thereby focusing and transferring the circuit pattern onto thewafer.

The illumination optical system 1262 is disposed in a planesubstantially conjugated with the pattern surface of the reticle 1263and includes a field stop defining an illumination area on the reticle1263, an aperture stop defining light amount distribution of theultraviolet light on a predetermined plane having substantially aFourier transform relationship with the pattern surface of the reticle1263 within the illumination optical system 1262, and a condenser lensfor illuminating the ultraviolet light emitted from the aperture stoponto the reticle 1263. In this case, in order to change or alter thelight amount distribution of the ultraviolet light on the predeterminedplane (Fourier transform plane), plural aperture stops having differentconfiguration and/or dimension may be provided on a turret, and one ofthe aperture stops selected in accordance with the pattern of thereticle 1263 may be located in a light path of the illumination opticalsystem 1262. Further, an optical integrator (homogenizer) may bedisposed between the wavelength converting portion of the ultravioletlaser apparatus 1261 and the field stop, and, when a fly-eye lens isused, the fly-eye lens may be arranged so that the emission focal planethereof substantially becomes a Fourier transform relationship with thepattern surface of the reticle 1263, and, when a rod integrator is used,the integrator may be arranged so that the emission plane thereofbecomes substantially in conjugation with the pattern surface of thereticle 1263.

Further, as a shutter for starting exposure of the exposure apparatus,the electro-optical modulating element or the acousto-optical modulatingelement (12, 22, 32) explained in connection with the first to thirdembodiments can be used. By switching the electro-optical modulatingelement or the acousto-optical modulating element from an OFF condition(i.e., condition (having great internal loss) that pulses are notgenerated) to an ON condition (i.e., a condition that the pulses aregenerated and the internal loss is reduced in a pulse pattern), theexposure is started. Further, in the exposure apparatus having theultraviolet laser apparatus 1261, the continuous light may be outputtedfrom the single-wavelength oscillating laser or the single-wavelengthoscillating laser may be pulse-oscillated. Particularly, in the latter,by using both current control of the single-wavelength oscillating laserand control of the electro-optical modulating element or theacousto-optical modulating element, oscillating interval, start and stopof the ultraviolet light (pulse light) illuminated onto the reticle 1263and the semiconductor wafer 1266 may be controlled. Further, in theexposure apparatus having the ultraviolet laser apparatus 1261 accordingto the illustrated embodiment, although it is not required forcontrolling an integrated amount of the ultraviolet light on the wafer2366 by means of the mechanical shutter, for example, when theultraviolet light is oscillated in order to stabilize the output (power,center wavelength, spectral bandwidth and the like) of the ultravioletlaser apparatus 1261, a shutter may be disposed within the illuminationlight path between the ultraviolet laser apparatus 1261 and the wafer1266, or a stage 1267 may be driven to displace the wafer 1266 from theultraviolet illumination area, in order to prevent the ultraviolet lightfrom reaching the wafer 1266 to photo-sensitize the photo-resist.

The semiconductor wafer 1266 is rested on the stage 1267 having a drivemechanism 1269. Whenever each exposure is completed, by shifting thestage 1267, each circuit pattern is transferred onto each of differentpositions on the semiconductor wafer. Such stage driving/exposure systemis referred to as a step-and-repeat system. As the stagedriving/exposure system other than the above, although there is astep-and-scan system in which the support member 1264 supporting thereticle 1263 is also provided with a drive mechanism and scan exposureis performed by shifting the reticle and the semiconductor wafer in asynchronous manner, the ultraviolet laser apparatus according to thepresent invention can also be applied to the step-and-scan system.

Further, in an exposure apparatus in which exposure is effected by usingultraviolet light, such as the exposure apparatus having the ultravioletlaser apparatus according to the present invention, normally, both theillumination optical system 1262 and the projection optical system 1265are constituted by quartz lenses with no chromatic aberrationcorrection. Further, particularly when the wavelength of the ultravioletlight is smaller than 200 nm, at least one of the plural refractionoptical elements constituting the projection optical system 1265 may beformed from fluorite, or a refraction/reflection optical system obtainedby combining at least one reflection optical element (concave mirror,mirror and the like) and the refraction optical element may be used.

As mentioned above, the exposure apparatus having the ultraviolet laserapparatus according to the present invention is more compact incomparison with other conventional exposure apparatuses (for example,exposure apparatus using an excimer laser or a solid-state laser) andhas high degree of freedom for arranging units constituting theapparatus since various elements are connected to the fibers. FIG. 20shows other embodiment in which such characteristics of the-ultravioletlaser apparatus according to the present invention are utilized.

In this embodiment, the laser light generating portion(single-wavelength laser, multiplexer) and the optical amplifier portiondescribed in the first, second or third embodiment, and the wavelengthconverting portion described in the fourth, fifth, sixth or seventhembodiment are arranged separately to form an exposure apparatus. Thatis to say, a wavelength converting portion 1272 is provided on a body ofthe exposure apparatus and other portions (laser light generatingportion, optical amplifier portion) 1271 of the ultraviolet laserapparatus are disposed outside of the body of the exposure apparatus,and these portions are connected to each other through a connectingfiber line 1273, thereby constituting the ultraviolet laser apparatus.Here, the connecting fiber line 1273 may be fiber themselves of fiberoptical amplifier (for example, fiber bundle 114 in the firstembodiment, and the like), non-doped fibers or a combination thereof.Further, portions of the body of the exposure apparatus other than theultraviolet laser apparatus can be constituted by using the sameelements as those shown in FIG. 19.

With this arrangement, main components generating heat such as anpumping semiconductor laser of the fiber optical amplifier, a drivepower supply of the semiconductor laser and a temperature controller canbe positioned outside of the body of the exposure apparatus.Accordingly, a problem based on heat, in which the body of the exposureapparatus is influenced by the heat from the ultraviolet laser apparatus(exposure light source) to deteriorate the alignment condition betweenthe optical axes can be suppressed.

By the way, as shown in FIG. 20, the reticle stage 1264 holding thereticle 1263 is designed to be shifted in X and Y directions by a drivemechanism 1268 and be rotated by a small angle. Further, a referencemark plate FM is provided on the wafer stage 1267, which reference markplate is used for baseline measurement which will be described later.Further, in the illustrated embodiment, there are provided an alignmentsystem 1280 for detecting alignment marks on the reticle 1263, andanother alignment system 1281 of off-axis type independently from theprojection optical system 1265.

The alignment system 1280 serves to illuminate the exposure illuminationlight or illumination light having the same wavelength (as that of saidexposure illumination light) onto the alignment marks on the reticle1263 and onto reference marks on the reference mark plate FM through theprojection optical system 1265 and to receive lights generated from bothmarks by an imaging element (CCD) to thereby detect their positionaldeviation. This alignment system is used for alignment of the reticle1263 and baseline measurement of the alignment system 1281. Thealignment system 1281 of off-axis type serves to illuminate white light(broad band light) for example having a spectral bandwidth of about 550to 750 nm onto the alignment marks on the semiconductor wafer 1266 andto focus both images of index marks provided within this system andimages of the alignment marks onto an imaging element (CCD) to therebydetect positional deviation between both marks. Further, when thealignment systems 1280, 1281 detect the reference marks on the referencemark plate FM, based on the result of its detection, an amount ofbaseline of the alignment system 1281 can be measured. Further, althoughthe baseline measurement is effected prior to exposure of thesemiconductor wafer, the baseline measurement may be performed each timethe semiconductor wafer is exchanged or the baseline measurement may beperformed each time several semiconductor wafers are exposed. However,the baseline measurement should always be effected after the reticle isexchanged.

In the illustrated embodiment, as a wavelength converting portionconnected to the ultraviolet laser apparatus (fundamental wavegenerating portion) 1271, the wavelength converting portion shown inFIG. 16 is used. That is to say, a wavelength converting portion 1272 onwhich the fundamental waves generated from four fiber bundle output ends851 are incident and a wavelength converting portion 1279 on which thefundamental wave generated from the fiber bundle output end 850 isincident are provided separately, and the wavelength converting portion1272 is integrally provided with a table for holding the illuminationoptical system 1262 and the wavelength converting portion 1279 isintegrally provided with a table for holding the alignment system 1280.In this case, a connecting fiber line 1278 is joined to the fiber bundleoutput end 850 to introduce the fundamental wave to the wavelengthconverting portion 1279. By doing so, it is not required that a lightsource for the alignment system 1280 be provided additionally and thereference marks can be detected by using illumination light having thesame wavelength as that of the exposure illumination light, therebypermitting high accuracy mark detection.

Further, in the illustrated embodiment, while an example that theillumination light having the same wavelength as that of the exposureillumination light is directed to the alignment system 1208 wasexplained, a wavelength longer than the wavelength (for example, 193 nm)of the exposure illumination light may be directed to the alignmentsystem 1280 or 1281. That is to say, among three stage wavelengthconverting portions shown in FIG. 16, for example, the pulse lightemitted from the second stage wavelength converting portion 853 may bedirected to the alignment system through the connecting fiber line.Further, a part of the pulse light emitted from the first stagewavelength converting portion 852 may be branched and the remainingpulse light may be wavelength-converted in the second stage wavelengthconverting portion 853 so that two pulse lights having differentwavelength emitted from two wavelength converting portions 852, 853 aredirected to the alignment system.

Further, the exposure apparatus shown in FIG. 20 includes a wavelengthcontrol device 1274 for controlling the oscillating wavelength of theDFB semiconductor laser (i.e., the wavelength of the ultraviolet light(exposure illumination light) illuminated onto the reticle 1263) byadjusting the temperature by using a temperature adjustor (for example,Peltier element) provided on a heat sink on which the single-wavelengthoscillating laser (for example, DFB semiconductor laser (11 in FIG. 1and the like)) within the fundamental wave generating portion 1271 isrested. The wavelength control device 1274 serves to effect bothstabilization of the center wavelength of the ultraviolet light andadjustment of optical properties (aberration, focal position, projectiondemagnification and the like) of the projection optical system 1265, bycontrolling the temperature of the DFB semiconductor laser so that thetemperature is changed at a unit of 0.001° C. With this arrangement, thewavelength stability of the ultraviolet light during the exposure of thesemiconductor wafer can be enhanced, and the optical properties of theprojection optical system 1265 which may be changed due to eitherillumination of the ultraviolet light or a change in atmosphericpressure can easily be adjusted.

The exposure apparatus shown in FIG. 20 further includes a pulse controlportion 1275 for applying driving voltage pulse to the opticalmodulating element (12 in FIG. 1 and the like) for converting thecontinuous light generated from the single-wavelength oscillating laser(DFB semiconductor laser) within the fundamental wave generating portion1271 into pulse light, an exposure control portion 1276 for calculatingthe number of pulses required for exposing the photo-resist, when thecircuit pattern is transferred, in accordance with the sensitivity ofthe photo-resist coated on the semiconductor wafer 1266 and forcontrolling the oscillating timing of the control pulse outputted fromthe pulse control portion 1275 and the magnitude of the control pulse inaccordance with the number of pulses, and a control device 1277 forcontrolling the entire exposure apparatus collectively.

The pulse control portion 1275 serves to control electric current of thesingle-wavelength oscillating laser (11 in FIG. 1 and the like) withinthe fundamental wave generating portion 1271 so that thesingle-wavelength oscillating laser can be pulse-oscillated. That is tosay, by the current control effected by the pulse control portion 1275,the single-wavelength oscillating laser can switch over the output ofthe continuous light and the pulse light. In the illustrated embodiment,the single-wavelength oscillating laser is pulse-oscillated, and only apart (having pulse width of about 10 to 20 ns) of the oscillated pulselight is picked up under the control of the above-mentioned opticalmodulating element (i.e., modulated to pulse light having pulse width of1 ns). As a result, in comparison with a case where the continuous lightis converted into the pulse light only by using the optical modulatingelement, pulse light having narrower pulse width can easily begenerated, and the oscillating interval of the pulse light andstart/stop of the oscillation of the pulse light can be controlled bythe exposure control portion 1276 more easily.

Further, the pulse control portion 1275 effects not only the switchingbetween the pulse oscillation and the continuous oscillation of thesingle-wavelength oscillating laser but also controlling of theoscillating interval and pulse width, upon pulse oscillation, andeffects at least one of the oscillation control of the single-wavelengthoscillating laser and control of the magnitude of voltage pulse appliedto the optical modulating element to compensate fluctuation in output ofthe pulse light. By doing this, the fluctuation in output of the pulselight caused upon changing the oscillating interval between the pulselights or upon restart of the pulse light can be compensated. That is tosay, the output (intensity) of the light can be maintained to asubstantially a constant value for each pulse.

Further, in the pulse control portion 1275, gain of at least one ofplural fiber optical amplifiers (13, 18, 19 in FIG. 1 and the like)arranged in serial within the fundamental wave generating portion 1271is adjusted, and intensity of the pulse light on the semiconductor wafercan be controlled only by the gain adjustment or by a combination of thegain adjustment and the control of the optical modulating element.Further, gain of at least one of the fiber optical amplifiers providedin parallel with respect to the plurality of channels divided inparallel in the multiplexer can be controlled similarly.

Further, the exposure control portion 1276 serves to detect thefundamental wave outputted from the fundamental wave generating portion1271 or the ultraviolet light outputted from the wavelength convertingportion 1272 or the pulse light outputted from, for example, the firstor second stage non-linear optical crystal within the wavelengthconverting portion 1272 and to control the pulse control portion 1275 onthe basis of the detected values (including intensity, wavelength andspectral bandwidth), thereby adjusting the oscillating interval of thepulse light, start/stop of the oscillation of the pulse light andintensity of the pulse light. Further, the detected values are inputtedto the wavelength control device 1274, where temperature control of thesingle-wavelength oscillating laser is effected on the basis of thedetected values to adjust the center wavelength and spectral bandwidthof the exposure illumination light (ultraviolet laser light).

The control device 1277 serves to send information regarding sensitivityof the photo-resist sent from a reading device (not shown) for readingan identifying mark (bar code and the like) provided on thesemiconductor wafer or a cassette holding the semiconductor wafer orinputted by the operator to the exposure control portion 1276, where thenumber of exposure pulses required for the pattern transferring iscalculated on the basis of the inputted information. Further, theexposure control portion 1276 controls the pulse control portion 1275 onthe basis of the number of exposure pulses and intensity of the pulselight determined in accordance with the pulse number, thereby adjustingthe oscillation timing and the magnitude of the control pulse applied tothe optical modulating element. As a result, the start/stop of theexposure and the intensity of the pulse light illuminated on thesemiconductor wafer 1266 are controlled, and the integrated light amountgiven to the photo-resist by the illumination of the plural pulse lightsis controlled to an optimum exposure amount corresponding to thesensitivity.

Further, the exposure control portion 1276 sends the command to thepulse control portion 1275 to cause the latter to effect the currentcontrol of the single-wavelength oscillating laser so that thestart/stop of the exposure (pulse oscillation) by the current controlalone or by a combination of the current control and the control of theoptical modulating element.

In the illustrated embodiment, when the laser apparatus shown in FIG. 1or FIG. 2 is used as the fundamental wave generating portion 1271, onepulse light picked up by the optical modulating element is divided intoplural (128 in number). In the illustrated embodiment, the divided 128pulse lights may be regarded as one pulse in total and the exposureamount control may be effected based on said one pulse in total or eachof the divided 128 pulse lights may be regarded as one pulserespectively and the exposure amount control may be effected based onsaid each pulse. Further, in the latter case, in place of the control ofthe optical modulating element effected by the pulse control portion1275, the intensity of the pulse light on the semiconductor wafer may becontrolled by adjusting the gain of the fiber optical amplifiers withinthe fundamental wave generating portion 1271 or a combination of thesetwo controls may be used.

Further, the exposure apparatus shown in FIG. 20 can effect the exposureof the semiconductor wafer by selectively switching the step-and-repeatsystem and the step-and-scan system. In the step-and-repeat system, thefield stop (reticle blind) within the illumination optical system 1262is driven to adjust the magnitude of the aperture so that the entirecircuit pattern on the reticle 1263 is illuminated by the exposureillumination light. On the other hand, in the step-and-scan system, theaperture of the field stop is adjusted so that the illumination area ofthe exposure illumination light within the circular projection field ofthe projection optical system 1265 is limited to be a rectangular slitextending along a direction perpendicular to the scanning direction forthe reticle 1263. Accordingly, in the step-and-scan system, since only apart of the circuit pattern on the reticle 1263 is illuminated, in orderto scan-expose the entire circuit pattern on the semiconductor wafer, insynchronous with the relative movement between the reticle 1263 and theexposure illumination light, the semiconductor wafer 1266 is shiftedrelative to the exposure illumination light at a speed ratiocorresponding to the projection demagnification of the projectionoptical system 1265.

By the way, in the exposure amount control upon the scan-exposure, byadjusting at least one of the pulse repeating frequency f defined by theoptical modulating element and the delay time between the channelsdefined by the TDM 23 shown in FIG. 2, the plurality of pulses areoscillated at equal time intervals from the fundamental wave generatingportion 1271 during the scan-exposure. Further, in accordance with thesensitivity property of the photoresist, by adjusting at least one ofthe intensity of the pulse light on the semiconductor wafer, scanningspeed of the semiconductor wafer, oscillation interval (frequency) ofthe pulse light, and the width of the pulse light (i.e., illuminationarea thereof) regarding the scanning direction of the semiconductorwafer, the integrated light amount of the plural pulse lightsilluminated while each point on the semiconductor wafer is moving acrossthe illumination area is controlled to the optimum exposure amount. Inthis case, in the exposure amount control, in consideration ofthrough-put, it is preferable that at least one of the intensity of thepulse light, oscillating frequency and width of the illumination area isadjusted, so that scanning speed of the semiconductor wafer isapproximately maintained so as to correspond to a highest speed of thewafer stage 1267.

Further, when the scan-exposure is effected by using the laser apparatusshown in FIG. 1 or FIG. 2, in the exposure amount control, it ispreferable that the divided 128 pulse lights are oscillated at equaltime intervals so that each of the divided pulses is one pulse. However,the 128 pulse lights may be regarded as one pulse and the exposureamount control may be performed so long as the 128 pulse lights can beregarded as one pulse (i.e., the shifting distance of the semiconductorwafer while the 128 pulse light are being illuminated does not become afactor for reducing accuracy of the exposure amount control) byadjusting the oscillation interval between the divided 128 pulse lightsin accordance with the scanning speed of the semiconductor wafer.

Further, in the above-mentioned various embodiments of the presentinvention, while the ultraviolet laser apparatus for outputting theoutput wavelength of 193 nm or 157 nm the same as that of the ArFexcimer laser or F₂ laser was explained, the present invention is notlimited to such an ultraviolet laser apparatus having such a wavelength,but can provide an ultraviolet laser apparatus capable of generating awavelength of 248 nm the same as that of the KrF excimer laser, byappropriately selecting arrangements of the laser generating portion,optical amplifier portion and wavelength converting portion.

For example, by using an ytterbium (Yb) doped fiber laser or asemiconductor laser capable of oscillating at a wavelength of 992 nm asthe single-wavelength oscillating laser in the laser generating portionand by using an ytterbium doped fiber optical amplifier is used as thefiber optical amplifier and by using an LBO crystal in the wavelengthconverting portion whereby the output from the fiber optical amplifieris subjected to second harmonic wave generation (wavelength of 496 nm)and 4th harmonic wave (wavelength of 248 nm) is further obtained fromthe resulting output by using a BBO crystal, the ultraviolet laserapparatus capable of generating a wavelength of 248 nm the same as thatof the KrF excimer laser can be provided.

Further, it is preferable that the fibers (including fiber opticalamplifiers) used in the above-mentioned embodiments are coated byTeflon. Although it is desirable that all of the fibers are subjected toTeflon coating, particularly, the fibers located within the chamber forhousing the body of the exposure apparatus are coated by Teflon. Thereason is that foreign matters (including fiber pieces and the like)generated from the fibers may become contaminant for contaminating theexposure apparatus. Thus, by providing the Teflon coating, fog ofoptical elements constituting the illumination optical system,projection optical system and alignment optical system, fluctuation intransmittance (reflection index) and/or optical properties (includingaberration) of these optical systems, and fluctuation in illuminance anddistribution thereof on the reticle or the semiconductor wafer, all ofwhich are caused by the contaminant, can be prevented. Further, in placeof the Teflon coating, the fibers housed in the chamber may collectivelybe enclosed by a stainless steel casing.

Further, a semiconductor device is manufactured by a step for effectingfunction/performance design thereof, a step for forming a reticle on thebasis of the designing step, a step for forming a wafer from Siliconematerial, a step for transferring a reticle pattern onto the wafer byusing the above-mentioned exposure apparatus, a step for assembling thedevice (including dicing step, bonding step and packaging step), and astep for checking the device. Further, the exposure apparatus can beused for manufacturing of a liquid crystal display, an imaging element(for example, CCD), a thin film magnetic head or a reticle, as well asmanufacturing of the semiconductor element.

Further, the exposure apparatus according to the illustrated embodimentcan be manufactured in such a manner that the illumination opticalsystem and the projection optical system (each constituted by aplurality of optical elements) are incorporated into the body of theexposure apparatus and optical adjustment thereof is effected, and thereticle stage and the wafer stage (each constituted by a plurality ofmechanical parts) are attached to the body of the exposure apparatus andwiring and piping are connected, and total adjustment (electricaladjustment, operation confirmation and the like) is effected. Further,in the above-mentioned exposure apparatus, the ultraviolet laserapparatus 1261 is attached to the body of the exposure apparatus, andparts (laser generating portion, optical amplifier and the like) of theultraviolet laser apparatus 1261 disposed outside of the body of theexposure apparatus are connected, via the fiber line, to the wavelengthconverting portion disposed within the body, and alignment between theoptical axes between the ultraviolet laser apparatus 1261 (wavelengthconverting portion) and the illumination optical system 1262 iseffected. Further, it is desirable that the exposure apparatus ismanufactured in a clean room in which a temperature and cleanness arecontrolled.

Further, in the ninth embodiment, while an example that the laserapparatus is applied to the exposure apparatus was explained, forexample, the laser apparatus according to the present invention can beapplied to a laser repairing apparatus used for cutting a part (fuse andthe like) of a circuit pattern formed on the wafer. Further, the laserapparatus according to the present invention can be applied to achecking apparatus using visible light or infrared light. In this case,it is not required that the wavelength converting portion described inconnection with the fourth, fifth, sixth or seventh embodiment beincorporated into the laser apparatus. That is to say, the presentinvention is effective to not only the ultraviolet laser apparatus butalso a laser apparatus having no wavelength converting portion andadapted to generate the fundamental wave having visible band or infraredband.

What is claimed is:
 1. An ultraviolet laser apparatus comprising: alaser generating portion having a single-wavelength oscillating laser,that generates laser light having a single wavelength within awavelength range from an infrared band to a visible band; a lightdividing device that divides or branches the laser light generated fromthe single-wavelength oscillating laser into plural lights; an opticalamplifier having a fiber optical amplifier that amplifies the plurallights from the light dividing device; and a wavelength convertingportion having a non-linear optical crystal that wavelength-converts theamplified plural lights into ultraviolet light; whereby ultravioletlight having a single wavelength is generated.
 2. The ultraviolet laserapparatus according to claim 1, wherein said single-wavelengthoscillating laser has an oscillating wavelength control device forcontrolling an oscillating wavelength of the laser light to be generatedto a constant wavelength.
 3. The ultraviolet laser apparatus accordingto claim 1, comprising a plurality of the optical amplifiers and arespective plurality of the wavelength converting portions.
 4. Theultraviolet laser apparatus according to claim 1, wherein said lightdividing device has a splitter for dividing or branching the laser lightgenerated by said single-wavelength oscillating laser into plural lightswhich are in parallel to each other; and said splitter is provided atits output side with fibers having different lengths.
 5. The ultravioletlaser apparatus according to claim 4, wherein the lengths of the fibershaving different lengths are selected so that delay intervals betweenthe laser lights branched in parallel at output ends of the fibersbecome substantially the same.
 6. The ultraviolet laser apparatusaccording to claim 5, wherein the lengths of the fibers having differentlengths are selected so that the delay interval between the laser lightsbranched in parallel at output ends of the fibers becomes a reciprocalof product of repetition frequency of the laser light incident on saidsplitter and the number of light paths branched in parallel by saidsplitter.
 7. The ultraviolet laser apparatus according to claim 1,wherein said light dividing device comprises a time divisionmultiplexer.
 8. The ultraviolet laser apparatus according to claim 1,wherein the output end of said optical amplifier provided at an incidentside of said wavelength converting portion is formed by expanding a coreat an output end of a fiber in a tapered fashion toward an output endface of the fiber.
 9. The ultraviolet laser apparatus according to claim1, wherein the output end of said optical amplifier provided at anincident side of said wavelength converting portion is provided with awindow member provided at an output end of a fiber and allowing thelaser light amplified by said optical amplifier to be transmittedtherethrough.
 10. The ultraviolet laser apparatus according to claim 1,wherein said optical amplifier comprises an erbium doped fiberamplifier.
 11. The ultraviolet laser apparatus according to claim 1,wherein said optical amplifier comprises a fiber optical amplifier dopedby erbium and ytterbium.
 12. The ultraviolet laser apparatus accordingto claim 1, wherein said optical amplifier includes a plurality of fiberoptical amplifiers for amplifying the plural lights branched by saidlight dividing device, respectively.
 13. The ultraviolet laser apparatusaccording to claim 12, wherein said optical amplifier includes a fiberoutput control device for controlling a pumping power of each of saidplurality of fiber optical amplifiers so that an output of theultraviolet light becomes a predetermined light output or light outputsamplified by said plurality of fiber optical amplifiers becomepredetermined light outputs.
 14. The ultraviolet laser apparatusaccording to claim 12, wherein the output end of said optical amplifierprovided at the incident side of said wavelength converting portion isformed by dividing the output ends of the plurality of fibers into oneoutput group or plural output groups and by bundling each of the outputgroups.
 15. The ultraviolet laser apparatus according to claim 14,wherein the output groups of said optical amplifier divided into theplural groups are constituted by a first output group formed by bundlingone or several fiber output ends, and second one or more plural outputgroups formed by either bundling the remaining fiber output ends otherthan the first output group to result in a single bundle output group orbundling each of plural output groups, obtained by dividing saidremaining fiber output ends other than the first output group, to resultin plural bundle output groups.
 16. The ultraviolet laser apparatusaccording to claim 15, wherein the output end of said optical amplifierprovided at the incident side of said wavelength converting portion haswindow members provided at the fiber output ends formed by bundling eachof the output groups, respectively and allowing the laser lightsamplified by said optical amplifier to be transmitted therethrough. 17.The ultraviolet laser apparatus according to claim 15, wherein saidwavelength converting portion is provided for each of said output groupsof said optical amplifier.
 18. The ultraviolet laser apparatus accordingto claim 1, wherein said wavelength converting portion is provided atits input side with a light collecting optical element for collectingand directing the laser light emitted from said optical amplifier intothe non-linear optical crystal.
 19. The ultraviolet laser apparatusaccording to claim 18, further comprising a light dividing or branchingdevice for dividing or branching the laser light into plural lights, andwherein said optical amplifier has a plurality of fiber output ends foremitting the plural branched light, and said light collecting element isprovided for each of said output groups obtained by dividing the pluralfiber output ends into plural groups and by bundling the divided groups.20. The ultraviolet laser apparatus according to claim 18, wherein aplurality of said light collecting optical elements are provided byforming output ends of the bundled output groups of said opticalamplifier as lenses, respectively.
 21. The ultraviolet laser apparatusaccording to claim 18, further comprising a light dividing or branchingdevice for dividing or branching the laser light into plural lights, andwherein said optical amplifier has a plurality of fiber output ends foremitting the plural branched light, and said light collecting element isprovided for each of the fiber output ends.
 22. The ultraviolet laserapparatus according to claim 21, further comprising a light dividing orbranching device for dividing or branching the laser light into plurallights, and wherein said optical amplifier has a plurality of fiberoutput ends for emitting the plural branched light, and said lightcollecting elements are provided by forming the plural fiber output endsas lenses, respectively.
 23. The ultraviolet laser apparatus accordingto claim 1, wherein said laser generating portion generates laser lighthaving a single wavelength of about 1.5 μm, and said wavelengthconverting portion generates ultraviolet light having an 8-times or10-times high harmonic wave which is obtained from a fundamental wavehaving said wavelength of about 1.5 μm outputted from said opticalamplifier.
 24. The ultraviolet laser apparatus according to claim 23,wherein said single-wavelength oscillating laser comprises a DFBsemiconductor laser or a fiber laser having an oscillating wavelengthfalling within a range from 1.51 μm to 1.59 μm, and said wavelengthconverting portion generates the 8-times high harmonic wave having awavelength falling within a range from 189 nm to 199 nm.
 25. Theultraviolet laser apparatus according to claim 24, wherein saidsingle-wavelength oscillating laser generates laser light having anoscillating wavelength falling within a range from 1.544 μm to 1.552 μm,and said wavelength converting portion generates the 8-times highharmonic wave having a wavelength falling within a range from 193 nm to194 nm which is substantially the same as an oscillating wavelength ofan ArF excimer laser.
 26. The ultraviolet laser apparatus according toclaim 23, wherein said wavelength converting portion has a firstnon-linear optical crystal for generating the 8-times high harmonic wavewith respect to the fundamental wave, which is obtained from thefundamental wave and a 7-times high harmonic wave with respect to thefundamental wave by sum frequency generation.
 27. The ultraviolet laserapparatus according to claim 26, wherein said wavelength convertingportion has a second non-linear optical crystal for generating a 2-timeshigh harmonic wave which is obtained from the fundamental wave throughsecondary high harmonic wave generation, a third non-linear opticalcrystal for generating a 3-times high harmonic wave with respect to thefundamental wave which is obtained from the fundamental wave and the2-times high harmonic wave by sum frequency generation, a fourthnon-linear optical crystal for generating a 4-times high harmonic wavewith respect to the fundamental wave which is obtained from the 2-timeshigh harmonic wave through secondary high harmonic wave generation, anda fifth non-linear optical crystal for generating the 7-times highharmonic wave with respect to the fundamental wave which is obtainedfrom the 3-times high harmonic wave and the 4-times high harmonic waveof the fundamental wave by sum frequency generation.
 28. The ultravioletlaser apparatus according to claim 27, wherein said first to fourthnon-linear optical crystals are LiB₃O₅ (LBO) crystal, and said fifthnon-linear optical crystal is either β-BaB₂O₄ (BBO) crystal or CsLiB₆O₁₀(CLBO) crystal.
 29. The ultraviolet laser apparatus according to claim23, wherein said single-wavelength oscillating laser comprises a DFBsemiconductor laser or a fiber laser having an oscillating wavelengthfalling within a range from 1.51 μm to 1.59 μm, and said wavelengthconverting portion generates a 10-times high harmonic wave having awavelength falling within a range from 151 nm to 159 nm.
 30. Theultraviolet laser apparatus according to claim 29, wherein saidsingle-wavelength oscillating laser generates laser light having anoscillating wavelength falling within a range from 1.57 μm to 1.58 μm,and said wavelength converting portion generates the 10-times highharmonic wave having a wavelength falling within a range from 157 nm to158 nm which is substantially the same as an oscillating wavelength ofan F₂ excimer laser.
 31. The ultraviolet laser apparatus according toclaim 1, wherein said laser generating portion generates laser lighthaving a single wavelength of about 1.1 μm, and said wavelengthconverting portion generates ultraviolet light having a 7-times highharmonic wave which is obtained from a fundamental wave having thewavelength of about 1.1 μm outputted from said optical amplifier. 32.The ultraviolet laser apparatus according to claim 31, wherein saidsingle-wavelength oscillating laser comprises a DFB semiconductor laseror a fiber laser having an oscillating wavelength falling within a rangefrom 1.03 μm to 1.12 μm, and said wavelength converting portiongenerates the 7-times high harmonic wave having a wavelength fallingwithin a range from 147 nm to 160 nm.
 33. The ultraviolet laserapparatus according to claim 32, wherein said single-wavelengthoscillating laser is an ytterbium doped fiber laser.
 34. The ultravioletlaser apparatus according to claim 31, wherein said single-wavelengthoscillating laser generates laser light having an oscillating wavelengthfalling within a range from 1.099 μm to 1.106 μm, and said wavelengthconverting portion generates the 7-times high harmonic wave having awavelength falling within a range from 157 nm to 158 nm which issubstantially the same as an oscillating wavelength of an F₂ excimerlaser.
 35. An exposure apparatus wherein: an ultraviolet laser apparatusaccording to claim 1 is used as a light source.
 36. The exposureapparatus according to claim 35, further comprising an illuminationoptical system for illuminating the ultraviolet light emitted from saidultraviolet laser apparatus onto a mask, and a projection optical systemfor projecting a pattern image of said mask transmitted therethrough orreflected thereon by illumination of the ultraviolet light, onto asubstrate.
 37. The exposure apparatus according to claim 35, whereinthere is provided said ultraviolet laser apparatus in which said opticalamplifier comprises a plurality of fiber optical amplifiers, and theoutput end of said optical amplifier has the plural output groups formedby dividing the plural fiber output ends and by bundling the dividedfiber output ends; and further wherein the ultraviolet light outputtedfrom at least one of the output groups is used as an alignment lightsource of the exposure apparatus.
 38. The exposure apparatus accordingto claim 35, further comprising a projection optical system forprojecting a pattern image of a mask onto a substrate, and a patterndetecting system for illuminating the ultraviolet light emitted fromsaid ultraviolet laser apparatus onto a mark pattern located on anobject side or on an image side of said projection optical system. 39.The apparatus according to claim 1, wherein said wavelength convertingportion generates light having a wavelength less than 200 nm as saidultraviolet light.
 40. The apparatus according to claim 39, wherein saidsingle-wavelength oscillating laser pulse-emits light having a firstpulse width, and said laser generating portion includes a lightmodulator that generates with the pulse-emitted light from saidsingle-wavelength oscillating laser pulse light having a second pulsewidth narrower than the first pulse width to generate the pulse light assaid laser light.
 41. An exposure apparatus comprising: a laserapparatus according to claim 39, and an illumination optical systemthrough which ultraviolet light generated from the laser apparatuspasses to illuminate a first object having a pattern with the light, asecond object being exposed with the illuminated pattern on the firstobject.
 42. The apparatus according to claim 41, further comprising anadjusting device connected with said laser apparatus, that detects lightdifferent from said ultraviolet light in said laser apparatus to adjustan emission property of said ultraviolet light by said laser apparatusbased on the detection.
 43. The apparatus according to claim 42, whereinsaid generating portion includes a light modulator that generates pulselight with light from said single-wavelength oscillating laser as saidlaser light, and wherein said adjusting device adjusts at least one ofintensity, center wavelength, wavelength width and oscillation intervalof said ultraviolet light by means of at least one of saidsingle-wavelength oscillating laser and said light modulator.
 44. Theapparatus according to claim 43, wherein said adjusting device adjustsor controls at least one of temperature and control parameters of saidsingle-wavelength oscillating laser, and control parameters of saidlight modulator.
 45. The apparatus according to claim 43, wherein saidadjusting device adjusts or controls intensity of ultraviolet light bymeans of said single-wavelength oscillating laser, said light modulatorand said optical amplifier.
 46. The apparatus according to claim 45,wherein said optical amplifier includes a different fiber opticalamplifier from said fiber optical amplifier, disposed between said lightdividing device and said fiber optical amplifier or between said opticalamplifier and said wavelength converting portion, and said adjustingdevice controls at least one of said fiber optical amplifier and saiddifferent fiber optical amplifier to adjust the intensity of saidultraviolet light.
 47. The apparatus according to claim 43, wherein saidadjusting device detects ultraviolet light generated from said laserapparatus and operates said adjusting operation based on the detectedresult.
 48. The apparatus according to claim 43, further comprising aprojection optical system to project an image of said illuminatedpattern onto said second object, and said adjusting device adjusts animage characteristics of the projection optical system by at least oneof said single-wavelength oscillating laser and said light modulator.49. The apparatus according to claim 41, wherein said laser apparatus isconstructed so that at least a portion of said light dividing device andsaid optical amplifier is exchangeable as a unit.
 50. The apparatusaccording to claim 41, further comprising a projection optical system toproject an image of said illuminated pattern onto said second object anda mark detecting system optically connected with said laser apparatus todetect through the projection optical system a mark illuminated withsaid ultraviolet light.
 51. The apparatus according to claim 41, whereinsaid laser apparatus is constructed so that at least said wavelengthconverting portion is integrally held together with at least a portionof said illumination optical system.
 52. The apparatus according toclaim 41, wherein said wavelength converting portion includes aplurality of non-linear optical crystals, at least one of which is usedfor NCPM (Non-Critical Phase Matching).
 53. The apparatus according toclaim 41, wherein said laser apparatus includes a temperaturecontrolling mechanism connected with said wavelength converting portionand wherein said wavelength converting portion includes a plurality ofnon-linear optical crystals, temperature of at least one of which iscontrolled.
 54. An exposure apparatus comprising: a light source unitprovided with a laser generating portion having a laser source and alight modulator to generate pulse light having a single wavelengthwithin a wavelength range from an infrared band to a visible band, alight dividing device that divides the generated pulse light into plurallights, an optical amplifier having a plurality of fiber opticalamplifiers that amplify the divided lights, respectively, and awavelength-converting portion having a non-linear optical crystal thatwavelength-converts the amplified lights into light having a wavelengthless than 200 nm; and an illumination optical system through which thelight generated from the light source unit passes to illuminate a firstobject having a pattern with the light, a second object being exposedwith the illuminated pattern on the first object.
 55. The exposureapparatus according to claim 54, wherein said laser source pulse-emitslight having a first pulse width and said light modulator generates thepulse light having a second pulse width narrower than the first pulsewidth with the pulse-emitted light.
 56. The exposure apparatus accordingto claim 55, wherein said light source has an optical device forreducing coherence of said divided lights.
 57. A laser apparatuscomprising: a light source for generating continuous light; an opticalmodulating device for converting the continuous light into pulse light;a first fiber optical amplifier for amplifying the pulse light; a secondfiber optical amplifier for amplifying the amplified pulse light; and alight dividing device disposed on an incident side of at least one ofthe first and second fiber optical amplifiers, and wherein pulse lightsdivided by the light dividing device are incident on a later stage fiberoptical amplifier.
 58. The laser apparatus according to claim 57,further comprising a delay device for directing divided plural pulselights into said fiber optical amplifier disposed at a later stage ofsaid light dividing or branching device with time delay.
 59. The laserapparatus according to claim 57, wherein said second fiber opticalamplifier comprises a large mode diameter fiber.
 60. The laser apparatusaccording to claim 57, wherein said first and second fiber opticalamplifiers comprise one of a quartz fiber, a silicate group fiber and afluoride group fiber.
 61. The laser apparatus according to claim 57,wherein the continuous light is infrared light or visible light, andfurther comprising a wavelength converting portion forwavelength-converting the pulse light amplified by said second opticalamplifier into ultraviolet light.
 62. The laser apparatus according toclaim 61, wherein said second optical amplifier comprises a ZBLAN fiber.63. An exposure method comprising the steps of: illuminating ultravioletlight emitted from a laser apparatus according to claim 61 onto a mask;and exposing a substrate with said ultraviolet light through said mask.64. The laser apparatus according to claim 57, further comprising atleast one third fiber optical amplifier disposed between said first andsecond fiber optical amplifiers.
 65. An exposure apparatus comprising: alaser apparatus according to claim 57; an illumination optical systemfor illuminating the pulse light amplified by said second fiber opticalamplifier onto a mask; and an adjusting device for adjusting at leastone of oscillation, intensity and wavelength of the pulse light.
 66. Theexposure apparatus according to claim 65, wherein said adjusting devicehas a first control device for controlling oscillation and magnitude ofa control pulse applied to said optical modulating element.
 67. Theexposure apparatus according to claim 66, wherein said adjusting devicehas a second control device for controlling a gain of at least one ofsaid first and second fiber optical amplifiers.
 68. The exposureapparatus according to claim 66, wherein said adjusting device has athird control device for controlling a temperature of said light source.69. The exposure apparatus according to claim 66, further comprising analignment system for detecting a mark on a substrate onto which apattern formed on a mask is transferred, and a transmission system fordirecting at least a part of the amplified pulse light to said alignmentsystem.
 70. The exposure apparatus according to claim 69, wherein saidtransmission system comprises first and second fibers for directing theamplified pulse light to said illumination optical system and saidalignment system, respectively.
 71. The exposure apparatus according toclaim 70, further comprising a plurality of wavelength convertingportions for wavelength-converting the amplified pulse light intoultraviolet light, and wherein, among said plurality of wavelengthconverting portions, a first wavelength converting portion is disposedbetween said second fiber optical amplifier and said first fiber orbetween said first fiber and said illumination optical system.
 72. Theexposure apparatus according to claim 71, wherein said first wavelengthconverting portion is disposed between said first fiber and saidillumination optical system and is integrally held together with atleast a part of said illumination optical system.
 73. The exposureapparatus according to claim 72, wherein, among said plurality ofwavelength converting portions, a second wavelength converting portionis disposed between said second fiber optical amplifier and said secondfiber or between said second fiber and said alignment system.
 74. Theexposure apparatus according to claim 73, wherein said second wavelengthconverting portion is disposed between said second fiber and saidalignment system and is integrally held together with at least a part ofsaid alignment system.
 75. The exposure apparatus according to claim 65,further comprising a projection optical system for projecting at least apart of a pattern formed on a mask onto a substrate, and a drivingdevice for shifting said mask and said substrate in a synchronous mannerat a speed substantially corresponding to a projection magnification ofsaid projection optical system in order to scan-expose the entirepattern on said substrate.
 76. The exposure apparatus according to claim65, wherein said adjusting device effects current control of said lightsource to pulse-oscillate said light source.
 77. A method formanufacturing a device, comprising: providing the exposure apparatusaccording to claim 65, and a step for transferring a pattern formed onsaid mask onto a substrate by using exposure apparatus according toclaim
 65. 78. The laser apparatus according to claim 57, wherein saidoptical modulating device oscillates said light source under currentcontrol, and a pulse width of the pulse light oscillated by said lightsource is reduced by an optical modulating element.
 79. The laserapparatus according to claim 57, further comprising a control device forcontrolling at least one of said light source and said opticalmodulating device to compensate the fluctuation in output of the pulselight outputted from said second fiber optical amplifier.
 80. Anexposure method comprising the steps of: converting continuous lightemitted from a light source into pulse light; amplifying the pulse lightby means of a first optical amplifier; amplifying the amplified pulselight by means of a second fiber optical amplifier; dividing the pulselight into plural lights at an incident side of at least one of thefirst and second fiber optical amplifiers, the pulse lights beingincident on a later stage fiber optical amplifier; illuminating a maskwith the pulse light from the second fiber optical amplifier; andexposing a substrate with the pulse light through said mask.
 81. Theexposure method according to claim 80, wherein said light sourcegenerates continuous light having infrared band or visible band, and thepulse light is wavelength-converted into ultraviolet light having awavelength less than 200 nm before the pulse light is illuminated ontosaid mask.
 82. The exposure method according to claim 81, wherein, priorto the exposure of said substrate, at least a part of the pulse light isilluminated onto a mark on said mask to detect positional information ofthe mark.
 83. The exposure method according to claim 81, wherein atemperature of said light source is adjusted to control a wavelength ofthe ultraviolet light.
 84. The exposure method according to claim 81,wherein at least one of an optical modulator that converts saidcontinuous light into pulse light and said first and second fiberoptical amplifiers is controlled to adjust intensity of the ultravioletlight.
 85. The exposure method according to claim 84, wherein repeatedfrequency of the pulse light defined by said optical modulator iscontrolled to adjust an oscillation interval of the ultraviolet light.86. The exposure method according to claim 85, wherein a time dividerdisposed between said optical modulator and one of said first and secondfiber optical amplifiers and adapted to time-divide the pulse light intoplural light is controlled to adjust the oscillation interval of theultraviolet light.
 87. A method for manufacturing a device, comprising:a step for transferring a device pattern onto said substrate by using anexposure method according to claim 80.